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	$18.61	5.300%	$19.5963	$19.60	$19.60	$19.60
Purchase #2	$151.34	9.841%	$166.2334	$166.23	$166.25	$166.20
Purchase #3	$111.44	12.433%	$125.2953	$125.30	$125.30	$125.30
Purchase #4	$209.66	12.699%	$236.2847	$236.28	$236.30	$236.30
Purchase #5	$54.40	12.674%	$61.2947	$61.29	$61.30	$61.30
Purchase #6	$75.74	3.690%	$78.5348	$78.53	$78.55	$78.50
Purchase #7	$47.33	11.387%	$52.7195	$52.72	$52.70	$52.70
7 purchase totals =	$668.52		$739.9587	$739.95	$740.00	$739.90