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	$100.54	9.548%	$110.1396	$110.14	$110.15	$110.10
Purchase #2	$246.34	7.766%	$265.4708	$265.47	$265.45	$265.50
Purchase #3	$113.94	13.136%	$128.9072	$128.91	$128.90	$128.90
Purchase #4	$211.74	6.434%	$225.3634	$225.36	$225.35	$225.40
Purchase #5	$50.97	3.121%	$52.5608	$52.56	$52.55	$52.60
Purchase #6	$11.31	3.704%	$11.7289	$11.73	$11.75	$11.70
Purchase #7	$186.73	5.205%	$196.4493	$196.45	$196.45	$196.40
7 purchase totals =	$921.57		$990.6200	$990.62	$990.60	$990.60