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	$236.86	12.658%	$266.8417	$266.84	$266.85	$266.80
Purchase #2	$164.91	9.256%	$180.1741	$180.17	$180.15	$180.20
Purchase #3	$223.57	13.439%	$253.6156	$253.62	$253.60	$253.60
Purchase #4	$172.28	7.529%	$185.251	$185.25	$185.25	$185.30
Purchase #5	$143.43	9.672%	$157.3025	$157.30	$157.30	$157.30
Purchase #6	$126.95	3.553%	$131.4605	$131.46	$131.45	$131.50
Purchase #7	$242.50	9.495%	$265.5254	$265.53	$265.55	$265.50
7 purchase totals =	$1,310.50		$1,440.1708	$1,440.17	$1,440.15	$1,440.20