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	$135.63	12.142%	$152.0982	$152.10	$152.10	$152.10
Purchase #2	$59.82	7.726%	$64.4417	$64.44	$64.45	$64.40
Purchase #3	$234.43	8.302%	$253.8924	$253.89	$253.90	$253.90
Purchase #4	$95.91	13.698%	$109.0478	$109.05	$109.05	$109.00
Purchase #5	$238.25	4.643%	$249.3119	$249.31	$249.30	$249.30
Purchase #6	$181.46	5.758%	$191.9085	$191.91	$191.90	$191.90
Purchase #7	$216.84	12.808%	$244.6129	$244.61	$244.60	$244.60
7 purchase totals =	$1,162.34		$1,265.3134	$1,265.31	$1,265.30	$1,265.20