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	$227.52	13.234%	$257.63	$257.63	$257.65	$257.60
Purchase #2	$229.84	11.684%	$256.6945	$256.69	$256.70	$256.70
Purchase #3	$57.93	5.265%	$60.98	$60.98	$61.00	$61.00
Purchase #4	$48.86	7.582%	$52.5646	$52.56	$52.55	$52.60
Purchase #5	$85.56	5.784%	$90.5088	$90.51	$90.50	$90.50
Purchase #6	$113.63	10.525%	$125.5896	$125.59	$125.60	$125.60
Purchase #7	$32.91	7.623%	$35.4187	$35.42	$35.40	$35.40
7 purchase totals =	$796.25		$879.3862	$879.38	$879.40	$879.40