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	$131.82	4.271%	$137.45	$137.45	$137.45	$137.50
Purchase #2	$166.94	3.150%	$172.1986	$172.20	$172.20	$172.20
Purchase #3	$26.50	10.607%	$29.3109	$29.31	$29.30	$29.30
Purchase #4	$21.94	11.615%	$24.4883	$24.49	$24.50	$24.50
Purchase #5	$106.58	5.816%	$112.7787	$112.78	$112.80	$112.80
Purchase #6	$151.35	12.626%	$170.4595	$170.46	$170.45	$170.50
Purchase #7	$190.44	11.382%	$212.1159	$212.12	$212.10	$212.10
7 purchase totals =	$795.57		$858.8019	$858.81	$858.80	$858.90