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	$250.46	9.188%	$273.4723	$273.47	$273.45	$273.50
Purchase #2	$100.73	10.549%	$111.356	$111.36	$111.35	$111.40
Purchase #3	$44.94	12.314%	$50.4739	$50.47	$50.45	$50.50
Purchase #4	$158.54	5.127%	$166.6683	$166.67	$166.65	$166.70
Purchase #5	$188.45	9.620%	$206.5789	$206.58	$206.60	$206.60
Purchase #6	$91.48	11.644%	$102.1319	$102.13	$102.15	$102.10
Purchase #7	$40.87	7.202%	$43.8135	$43.81	$43.80	$43.80
7 purchase totals =	$875.47		$954.4948	$954.49	$954.45	$954.60