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	$125.32	13.842%	$142.6668	$142.67	$142.65	$142.70
Purchase #2	$200.25	11.593%	$223.465	$223.47	$223.45	$223.50
Purchase #3	$223.91	9.200%	$244.5097	$244.51	$244.50	$244.50
Purchase #4	$48.79	4.103%	$50.7919	$50.79	$50.80	$50.80
Purchase #5	$244.28	9.829%	$268.2903	$268.29	$268.30	$268.30
Purchase #6	$246.70	11.612%	$275.3468	$275.35	$275.35	$275.30
Purchase #7	$33.83	3.853%	$35.1335	$35.13	$35.15	$35.10
7 purchase totals =	$1,123.08		$1,240.2040	$1,240.21	$1,240.20	$1,240.20