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	$83.51	7.801%	$90.0246	$90.02	$90.00	$90.00
Purchase #2	$51.92	3.140%	$53.5503	$53.55	$53.55	$53.60
Purchase #3	$140.70	13.140%	$159.188	$159.19	$159.20	$159.20
Purchase #4	$205.71	13.376%	$233.2258	$233.23	$233.25	$233.20
Purchase #5	$215.75	9.242%	$235.6896	$235.69	$235.70	$235.70
Purchase #6	$208.77	3.844%	$216.7951	$216.80	$216.80	$216.80
Purchase #7	$244.87	10.610%	$270.8507	$270.85	$270.85	$270.90
7 purchase totals =	$1,151.23		$1,259.3241	$1,259.33	$1,259.35	$1,259.40