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	$47.75	4.715%	$50.0014	$50.00	$50.00	$50.00
Purchase #2	$111.48	3.693%	$115.597	$115.60	$115.60	$115.60
Purchase #3	$172.64	4.287%	$180.0411	$180.04	$180.05	$180.00
Purchase #4	$142.75	12.821%	$161.052	$161.05	$161.05	$161.10
Purchase #5	$161.43	4.575%	$168.8154	$168.82	$168.80	$168.80
Purchase #6	$195.60	11.169%	$217.4466	$217.45	$217.45	$217.40
Purchase #7	$43.45	4.787%	$45.53	$45.53	$45.55	$45.50
7 purchase totals =	$875.10		$938.4835	$938.49	$938.50	$938.40