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	$138.86	5.624%	$146.6695	$146.67	$146.65	$146.70
Purchase #2	$166.33	13.168%	$188.2323	$188.23	$188.25	$188.20
Purchase #3	$89.34	11.445%	$99.565	$99.57	$99.55	$99.60
Purchase #4	$217.51	10.234%	$239.77	$239.77	$239.75	$239.80
Purchase #5	$169.79	9.165%	$185.3513	$185.35	$185.35	$185.40
Purchase #6	$137.97	5.766%	$145.9254	$145.93	$145.95	$145.90
Purchase #7	$76.79	3.261%	$79.2941	$79.29	$79.30	$79.30
7 purchase totals =	$996.59		$1,084.8076	$1,084.81	$1,084.80	$1,084.90