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	$54.30	8.342%	$58.8297	$58.83	$58.85	$58.80
Purchase #2	$85.54	5.272%	$90.0497	$90.05	$90.05	$90.00
Purchase #3	$243.32	4.428%	$254.0942	$254.09	$254.10	$254.10
Purchase #4	$72.42	11.698%	$80.8917	$80.89	$80.90	$80.90
Purchase #5	$221.29	10.209%	$243.8815	$243.88	$243.90	$243.90
Purchase #6	$68.34	13.314%	$77.4388	$77.44	$77.45	$77.40
Purchase #7	$121.47	13.204%	$137.5089	$137.51	$137.50	$137.50
7 purchase totals =	$866.68		$942.6945	$942.69	$942.75	$942.60