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	$120.66	12.348%	$135.5591	$135.56	$135.55	$135.60
Purchase #2	$64.44	4.632%	$67.4249	$67.42	$67.40	$67.40
Purchase #3	$149.71	6.122%	$158.8752	$158.88	$158.90	$158.90
Purchase #4	$100.98	10.333%	$111.4143	$111.41	$111.40	$111.40
Purchase #5	$128.47	13.576%	$145.9111	$145.91	$145.90	$145.90
Purchase #6	$209.37	8.820%	$227.8364	$227.84	$227.85	$227.80
Purchase #7	$155.31	13.352%	$176.047	$176.05	$176.05	$176.00
7 purchase totals =	$928.94		$1,023.0680	$1,023.07	$1,023.05	$1,023.00