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	$229.47	9.414%	$251.0723	$251.07	$251.05	$251.10
Purchase #2	$35.88	11.674%	$40.0686	$40.07	$40.05	$40.10
Purchase #3	$246.46	9.687%	$270.3346	$270.33	$270.35	$270.30
Purchase #4	$155.91	10.427%	$172.1667	$172.17	$172.15	$172.20
Purchase #5	$134.29	12.656%	$151.2857	$151.29	$151.30	$151.30
Purchase #6	$234.90	8.344%	$254.5001	$254.50	$254.50	$254.50
Purchase #7	$107.69	3.513%	$111.4731	$111.47	$111.45	$111.50
7 purchase totals =	$1,144.60		$1,250.9011	$1,250.90	$1,250.85	$1,251.00