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	$18.78	7.612%	$20.2095	$20.21	$20.20	$20.20
Purchase #2	$248.36	11.362%	$276.5787	$276.58	$276.60	$276.60
Purchase #3	$42.25	10.154%	$46.5401	$46.54	$46.55	$46.50
Purchase #4	$188.67	12.816%	$212.8499	$212.85	$212.85	$212.80
Purchase #5	$42.35	10.459%	$46.7794	$46.78	$46.80	$46.80
Purchase #6	$131.90	7.343%	$141.5854	$141.59	$141.60	$141.60
Purchase #7	$61.35	8.533%	$66.585	$66.59	$66.60	$66.60
7 purchase totals =	$733.66		$811.1280	$811.14	$811.20	$811.10