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	$83.70	8.468%	$90.7877	$90.79	$90.80	$90.80
Purchase #2	$35.63	13.541%	$40.4547	$40.45	$40.45	$40.50
Purchase #3	$63.45	13.326%	$71.9053	$71.91	$71.90	$71.90
Purchase #4	$90.50	10.781%	$100.2568	$100.26	$100.25	$100.30
Purchase #5	$76.59	8.843%	$83.3629	$83.36	$83.35	$83.40
Purchase #6	$54.98	11.709%	$61.4176	$61.42	$61.40	$61.40
Purchase #7	$44.40	4.837%	$46.5476	$46.55	$46.55	$46.50
7 purchase totals =	$449.25		$494.7326	$494.74	$494.70	$494.80