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	$17.83	11.682%	$19.9129	$19.91	$19.90	$19.90
Purchase #2	$55.83	5.744%	$59.0369	$59.04	$59.05	$59.00
Purchase #3	$37.90	11.249%	$42.1634	$42.16	$42.15	$42.20
Purchase #4	$26.90	4.497%	$28.1097	$28.11	$28.10	$28.10
Purchase #5	$54.96	8.227%	$59.4816	$59.48	$59.50	$59.50
Purchase #6	$201.29	13.407%	$228.277	$228.28	$228.30	$228.30
Purchase #7	$50.74	8.262%	$54.9321	$54.93	$54.95	$54.90
7 purchase totals =	$445.45		$491.9136	$491.91	$491.95	$491.90