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	$13.75	9.146%	$15.0076	$15.01	$15.00	$15.00
Purchase #2	$75.53	3.369%	$78.0746	$78.07	$78.05	$78.10
Purchase #3	$50.50	3.645%	$52.3407	$52.34	$52.35	$52.30
Purchase #4	$163.55	3.576%	$169.3985	$169.40	$169.40	$169.40
Purchase #5	$110.72	13.476%	$125.6406	$125.64	$125.65	$125.60
Purchase #6	$139.45	10.800%	$154.5106	$154.51	$154.50	$154.50
Purchase #7	$119.45	6.740%	$127.5009	$127.50	$127.50	$127.50
7 purchase totals =	$672.95		$722.4735	$722.47	$722.45	$722.40