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	$195.45	11.188%	$217.3169	$217.32	$217.30	$217.30
Purchase #2	$220.95	10.327%	$243.7675	$243.77	$243.75	$243.80
Purchase #3	$229.83	13.263%	$260.3124	$260.31	$260.30	$260.30
Purchase #4	$213.80	13.874%	$243.4626	$243.46	$243.45	$243.50
Purchase #5	$38.40	13.105%	$43.4323	$43.43	$43.45	$43.40
Purchase #6	$213.82	4.527%	$223.4996	$223.50	$223.50	$223.50
Purchase #7	$45.36	3.334%	$46.8723	$46.87	$46.85	$46.90
7 purchase totals =	$1,157.61		$1,278.6636	$1,278.66	$1,278.60	$1,278.70