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	$39.51	3.811%	$41.0157	$41.02	$41.00	$41.00
Purchase #2	$67.49	4.802%	$70.7309	$70.73	$70.75	$70.70
Purchase #3	$242.25	5.821%	$256.3514	$256.35	$256.35	$256.40
Purchase #4	$105.72	7.485%	$113.6331	$113.63	$113.65	$113.60
Purchase #5	$105.71	10.357%	$116.6584	$116.66	$116.65	$116.70
Purchase #6	$203.50	11.804%	$227.5211	$227.52	$227.50	$227.50
Purchase #7	$236.88	8.251%	$256.425	$256.43	$256.45	$256.40
7 purchase totals =	$1,001.06		$1,082.3356	$1,082.34	$1,082.35	$1,082.30