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	$91.90	3.798%	$95.3904	$95.39	$95.40	$95.40
Purchase #2	$76.72	8.468%	$83.2166	$83.22	$83.20	$83.20
Purchase #3	$74.30	4.568%	$77.694	$77.69	$77.70	$77.70
Purchase #4	$247.67	3.492%	$256.3186	$256.32	$256.30	$256.30
Purchase #5	$33.75	4.134%	$35.1452	$35.15	$35.15	$35.10
Purchase #6	$50.87	11.122%	$56.5278	$56.53	$56.55	$56.50
Purchase #7	$50.57	10.367%	$55.8126	$55.81	$55.80	$55.80
7 purchase totals =	$625.78		$660.1052	$660.11	$660.10	$660.00