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	$153.69	12.267%	$172.5432	$172.54	$172.55	$172.50
Purchase #2	$172.55	7.240%	$185.0426	$185.04	$185.05	$185.00
Purchase #3	$248.36	3.142%	$256.1635	$256.16	$256.15	$256.20
Purchase #4	$64.72	11.811%	$72.3641	$72.36	$72.35	$72.40
Purchase #5	$97.45	12.273%	$109.41	$109.41	$109.40	$109.40
Purchase #6	$250.78	8.608%	$272.3671	$272.37	$272.35	$272.40
Purchase #7	$110.41	11.250%	$122.8311	$122.83	$122.85	$122.80
7 purchase totals =	$1,097.96		$1,190.7216	$1,190.71	$1,190.70	$1,190.70