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	$81.88	10.612%	$90.5691	$90.57	$90.55	$90.60
Purchase #2	$124.41	13.432%	$141.1208	$141.12	$141.10	$141.10
Purchase #3	$243.67	11.477%	$271.636	$271.64	$271.65	$271.60
Purchase #4	$225.59	12.427%	$253.6241	$253.62	$253.60	$253.60
Purchase #5	$37.95	13.544%	$43.0899	$43.09	$43.10	$43.10
Purchase #6	$209.51	8.715%	$227.7688	$227.77	$227.75	$227.80
Purchase #7	$162.63	6.239%	$172.7765	$172.78	$172.80	$172.80
7 purchase totals =	$1,085.64		$1,200.5852	$1,200.59	$1,200.55	$1,200.60