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	$28.80	11.504%	$32.1132	$32.11	$32.10	$32.10
Purchase #2	$78.85	11.572%	$87.9745	$87.97	$87.95	$88.00
Purchase #3	$166.95	8.324%	$180.8469	$180.85	$180.85	$180.80
Purchase #4	$26.30	12.634%	$29.6227	$29.62	$29.60	$29.60
Purchase #5	$62.62	12.263%	$70.2991	$70.30	$70.30	$70.30
Purchase #6	$82.84	8.803%	$90.1324	$90.13	$90.15	$90.10
Purchase #7	$169.27	4.339%	$176.6146	$176.61	$176.60	$176.60
7 purchase totals =	$615.63		$667.6034	$667.59	$667.55	$667.50