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	$108.47	3.484%	$112.2491	$112.25	$112.25	$112.20
Purchase #2	$55.51	7.249%	$59.5339	$59.53	$59.55	$59.50
Purchase #3	$150.39	10.429%	$166.0742	$166.07	$166.05	$166.10
Purchase #4	$44.65	3.401%	$46.1685	$46.17	$46.15	$46.20
Purchase #5	$71.59	11.231%	$79.6303	$79.63	$79.65	$79.60
Purchase #6	$11.63	3.750%	$12.0661	$12.07	$12.05	$12.10
Purchase #7	$196.52	6.468%	$209.2309	$209.23	$209.25	$209.20
7 purchase totals =	$638.76		$684.9530	$684.95	$684.95	$684.90