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	$101.83	9.607%	$111.6128	$111.61	$111.60	$111.60
Purchase #2	$29.91	7.845%	$32.2564	$32.26	$32.25	$32.30
Purchase #3	$83.29	9.363%	$91.0884	$91.09	$91.10	$91.10
Purchase #4	$91.59	12.645%	$103.1716	$103.17	$103.15	$103.20
Purchase #5	$88.50	13.389%	$100.3493	$100.35	$100.35	$100.30
Purchase #6	$220.49	12.216%	$247.4251	$247.43	$247.45	$247.40
Purchase #7	$187.90	11.249%	$209.0369	$209.04	$209.05	$209.00
7 purchase totals =	$803.51		$894.9405	$894.95	$894.95	$894.90