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	$139.83	12.167%	$156.8431	$156.84	$156.85	$156.80
Purchase #2	$142.60	11.830%	$159.4696	$159.47	$159.45	$159.50
Purchase #3	$143.46	5.451%	$151.28	$151.28	$151.30	$151.30
Purchase #4	$113.59	13.507%	$128.9326	$128.93	$128.95	$128.90
Purchase #5	$72.39	7.614%	$77.9018	$77.90	$77.90	$77.90
Purchase #6	$129.79	8.195%	$140.4263	$140.43	$140.45	$140.40
Purchase #7	$156.84	12.417%	$176.3148	$176.31	$176.30	$176.30
7 purchase totals =	$898.50		$991.1682	$991.16	$991.20	$991.10