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	$227.92	3.386%	$235.6374	$235.64	$235.65	$235.60
Purchase #2	$185.82	11.192%	$206.617	$206.62	$206.60	$206.60
Purchase #3	$29.74	9.448%	$32.5498	$32.55	$32.55	$32.50
Purchase #4	$112.63	9.266%	$123.0663	$123.07	$123.05	$123.10
Purchase #5	$139.46	6.549%	$148.5932	$148.59	$148.60	$148.60
Purchase #6	$121.94	12.773%	$137.5154	$137.52	$137.50	$137.50
Purchase #7	$40.52	13.797%	$46.1105	$46.11	$46.10	$46.10
7 purchase totals =	$858.03		$930.0896	$930.10	$930.05	$930.00