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	$204.96	8.207%	$221.7811	$221.78	$221.80	$221.80
Purchase #2	$34.97	6.516%	$37.2486	$37.25	$37.25	$37.20
Purchase #3	$222.77	9.323%	$243.5388	$243.54	$243.55	$243.50
Purchase #4	$170.31	4.793%	$178.473	$178.47	$178.45	$178.50
Purchase #5	$121.78	10.374%	$134.4135	$134.41	$134.40	$134.40
Purchase #6	$132.94	4.683%	$139.1656	$139.17	$139.15	$139.20
Purchase #7	$19.98	9.530%	$21.8841	$21.88	$21.90	$21.90
7 purchase totals =	$907.71		$976.5047	$976.50	$976.50	$976.50