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	$161.45	11.281%	$179.6632	$179.66	$179.65	$179.70
Purchase #2	$171.35	10.191%	$188.8123	$188.81	$188.80	$188.80
Purchase #3	$82.79	8.483%	$89.8131	$89.81	$89.80	$89.80
Purchase #4	$32.61	10.306%	$35.9708	$35.97	$35.95	$36.00
Purchase #5	$230.45	13.168%	$260.7957	$260.80	$260.80	$260.80
Purchase #6	$243.86	4.454%	$254.7215	$254.72	$254.70	$254.70
Purchase #7	$173.82	3.845%	$180.5034	$180.50	$180.50	$180.50
7 purchase totals =	$1,096.33		$1,190.2800	$1,190.27	$1,190.20	$1,190.30