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	$166.61	13.332%	$188.8224	$188.82	$188.80	$188.80
Purchase #2	$213.50	13.601%	$242.5381	$242.54	$242.55	$242.50
Purchase #3	$147.95	12.580%	$166.5621	$166.56	$166.55	$166.60
Purchase #4	$213.53	11.841%	$238.8141	$238.81	$238.80	$238.80
Purchase #5	$47.80	12.411%	$53.7325	$53.73	$53.75	$53.70
Purchase #6	$158.30	8.694%	$172.0626	$172.06	$172.05	$172.10
Purchase #7	$243.72	4.739%	$255.2699	$255.27	$255.25	$255.30
7 purchase totals =	$1,191.41		$1,317.8017	$1,317.79	$1,317.75	$1,317.80