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	$139.33	11.634%	$155.5397	$155.54	$155.55	$155.50
Purchase #2	$204.60	5.840%	$216.5486	$216.55	$216.55	$216.50
Purchase #3	$64.29	9.660%	$70.5004	$70.50	$70.50	$70.50
Purchase #4	$100.42	11.414%	$111.8819	$111.88	$111.90	$111.90
Purchase #5	$224.56	13.711%	$255.3494	$255.35	$255.35	$255.30
Purchase #6	$225.46	5.431%	$237.7047	$237.70	$237.70	$237.70
Purchase #7	$225.26	11.321%	$250.7617	$250.76	$250.75	$250.80
7 purchase totals =	$1,183.92		$1,298.2864	$1,298.28	$1,298.30	$1,298.20