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	$81.59	4.299%	$85.0976	$85.10	$85.10	$85.10
Purchase #2	$35.77	13.709%	$40.6737	$40.67	$40.65	$40.70
Purchase #3	$223.47	9.504%	$244.7086	$244.71	$244.70	$244.70
Purchase #4	$41.84	8.869%	$45.5508	$45.55	$45.55	$45.60
Purchase #5	$66.61	8.747%	$72.4364	$72.44	$72.45	$72.40
Purchase #6	$80.68	12.237%	$90.5528	$90.55	$90.55	$90.60
Purchase #7	$139.51	6.161%	$148.1052	$148.11	$148.10	$148.10
7 purchase totals =	$669.47		$727.1251	$727.13	$727.10	$727.20