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	$246.37	4.252%	$256.8457	$256.85	$256.85	$256.80
Purchase #2	$128.59	5.507%	$135.6715	$135.67	$135.65	$135.70
Purchase #3	$87.77	11.680%	$98.0215	$98.02	$98.00	$98.00
Purchase #4	$120.53	8.195%	$130.4074	$130.41	$130.40	$130.40
Purchase #5	$100.31	11.819%	$112.1656	$112.17	$112.15	$112.20
Purchase #6	$50.82	9.711%	$55.7551	$55.76	$55.75	$55.80
Purchase #7	$234.89	8.775%	$255.5016	$255.50	$255.50	$255.50
7 purchase totals =	$969.28		$1,044.3684	$1,044.38	$1,044.30	$1,044.40