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	$38.58	7.589%	$41.5078	$41.51	$41.50	$41.50
Purchase #2	$85.72	10.679%	$94.874	$94.87	$94.85	$94.90
Purchase #3	$42.68	4.186%	$44.4666	$44.47	$44.45	$44.50
Purchase #4	$228.77	12.815%	$258.0869	$258.09	$258.10	$258.10
Purchase #5	$208.69	9.273%	$228.0418	$228.04	$228.05	$228.00
Purchase #6	$58.79	4.386%	$61.3685	$61.37	$61.35	$61.40
Purchase #7	$148.36	9.603%	$162.607	$162.61	$162.60	$162.60
7 purchase totals =	$811.59		$890.9526	$890.96	$890.90	$891.00