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	$78.34	6.116%	$83.1313	$83.13	$83.15	$83.10
Purchase #2	$79.58	3.375%	$82.2658	$82.27	$82.25	$82.30
Purchase #3	$81.26	11.344%	$90.4781	$90.48	$90.50	$90.50
Purchase #4	$233.62	5.808%	$247.1886	$247.19	$247.20	$247.20
Purchase #5	$197.49	3.240%	$203.8887	$203.89	$203.90	$203.90
Purchase #6	$152.98	8.844%	$166.5096	$166.51	$166.50	$166.50
Purchase #7	$44.28	9.592%	$48.5273	$48.53	$48.55	$48.50
7 purchase totals =	$867.55		$921.9894	$922.00	$922.05	$922.00