Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$79.91	12.819%	$90.1537	$90.15	$90.15	$90.20
Purchase #2	$129.65	6.225%	$137.7207	$137.72	$137.70	$137.70
Purchase #3	$80.49	13.343%	$91.2298	$91.23	$91.25	$91.20
Purchase #4	$180.43	5.346%	$190.0758	$190.08	$190.10	$190.10
Purchase #5	$102.37	8.309%	$110.8759	$110.88	$110.90	$110.90
Purchase #6	$127.83	3.729%	$132.5968	$132.60	$132.60	$132.60
Purchase #7	$121.78	4.446%	$127.1943	$127.19	$127.20	$127.20
7 purchase totals =	$822.46		$879.8470	$879.85	$879.90	$879.90