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	$35.39	6.198%	$37.5835	$37.58	$37.60	$37.60
Purchase #2	$143.29	8.727%	$155.7949	$155.79	$155.80	$155.80
Purchase #3	$136.76	13.113%	$154.6933	$154.69	$154.70	$154.70
Purchase #4	$230.61	5.200%	$242.6017	$242.60	$242.60	$242.60
Purchase #5	$102.66	8.813%	$111.7074	$111.71	$111.70	$111.70
Purchase #6	$122.88	3.124%	$126.7188	$126.72	$126.70	$126.70
Purchase #7	$235.47	11.175%	$261.7838	$261.78	$261.80	$261.80
7 purchase totals =	$1,007.06		$1,090.8834	$1,090.87	$1,090.90	$1,090.90