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	$232.79	7.741%	$250.8103	$250.81	$250.80	$250.80
Purchase #2	$51.61	5.521%	$54.4594	$54.46	$54.45	$54.50
Purchase #3	$14.57	9.244%	$15.9169	$15.92	$15.90	$15.90
Purchase #4	$228.61	5.259%	$240.6326	$240.63	$240.65	$240.60
Purchase #5	$88.63	12.325%	$99.5536	$99.55	$99.55	$99.60
Purchase #6	$11.38	13.110%	$12.8719	$12.87	$12.85	$12.90
Purchase #7	$117.56	5.759%	$124.3303	$124.33	$124.35	$124.30
7 purchase totals =	$745.15		$798.5750	$798.57	$798.55	$798.60