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	$91.55	9.814%	$100.5347	$100.53	$100.55	$100.50
Purchase #2	$89.44	11.830%	$100.0208	$100.02	$100.00	$100.00
Purchase #3	$35.42	10.668%	$39.1986	$39.20	$39.20	$39.20
Purchase #4	$198.79	10.399%	$219.4622	$219.46	$219.45	$219.50
Purchase #5	$9.69	4.469%	$10.123	$10.12	$10.10	$10.10
Purchase #6	$158.79	8.749%	$172.6825	$172.68	$172.70	$172.70
Purchase #7	$88.28	3.859%	$91.6867	$91.69	$91.70	$91.70
7 purchase totals =	$671.96		$733.7085	$733.70	$733.70	$733.70