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	$91.44	9.646%	$100.2603	$100.26	$100.25	$100.30
Purchase #2	$153.88	8.281%	$166.6228	$166.62	$166.60	$166.60
Purchase #3	$58.29	12.433%	$65.5372	$65.54	$65.55	$65.50
Purchase #4	$170.43	4.205%	$177.5966	$177.60	$177.60	$177.60
Purchase #5	$124.76	12.782%	$140.7068	$140.71	$140.70	$140.70
Purchase #6	$52.69	13.217%	$59.654	$59.65	$59.65	$59.70
Purchase #7	$132.56	7.758%	$142.844	$142.84	$142.85	$142.80
7 purchase totals =	$784.05		$853.2217	$853.22	$853.20	$853.20