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	$73.40	7.581%	$78.9645	$78.96	$78.95	$79.00
Purchase #2	$56.30	3.262%	$58.1365	$58.14	$58.15	$58.10
Purchase #3	$140.25	8.244%	$151.8122	$151.81	$151.80	$151.80
Purchase #4	$24.82	7.820%	$26.7609	$26.76	$26.75	$26.80
Purchase #5	$124.63	13.510%	$141.4675	$141.47	$141.45	$141.50
Purchase #6	$52.76	13.487%	$59.8757	$59.88	$59.90	$59.90
Purchase #7	$231.34	11.671%	$258.3397	$258.34	$258.35	$258.30
7 purchase totals =	$703.50		$775.3570	$775.36	$775.35	$775.40