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	$248.89	10.508%	$275.0434	$275.04	$275.05	$275.00
Purchase #2	$76.55	7.659%	$82.413	$82.41	$82.40	$82.40
Purchase #3	$118.81	7.605%	$127.8455	$127.85	$127.85	$127.80
Purchase #4	$15.91	10.175%	$17.5288	$17.53	$17.55	$17.50
Purchase #5	$96.65	4.869%	$101.3559	$101.36	$101.35	$101.40
Purchase #6	$45.54	11.843%	$50.9333	$50.93	$50.95	$50.90
Purchase #7	$196.27	3.632%	$203.3985	$203.40	$203.40	$203.40
7 purchase totals =	$798.62		$858.5184	$858.52	$858.55	$858.40