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	$243.89	4.674%	$255.2894	$255.29	$255.30	$255.30
Purchase #2	$156.37	7.871%	$168.6779	$168.68	$168.70	$168.70
Purchase #3	$160.31	13.555%	$182.04	$182.04	$182.05	$182.00
Purchase #4	$178.59	5.456%	$188.3339	$188.33	$188.35	$188.30
Purchase #5	$189.96	11.389%	$211.5945	$211.59	$211.60	$211.60
Purchase #6	$226.71	10.789%	$251.1697	$251.17	$251.15	$251.20
Purchase #7	$61.32	7.133%	$65.694	$65.69	$65.70	$65.70
7 purchase totals =	$1,217.15		$1,322.7994	$1,322.79	$1,322.85	$1,322.80