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	$247.53	3.596%	$256.4312	$256.43	$256.45	$256.40
Purchase #2	$84.61	11.467%	$94.3122	$94.31	$94.30	$94.30
Purchase #3	$49.34	7.849%	$53.2127	$53.21	$53.20	$53.20
Purchase #4	$169.58	7.785%	$182.7818	$182.78	$182.80	$182.80
Purchase #5	$176.69	13.218%	$200.0449	$200.04	$200.05	$200.00
Purchase #6	$248.45	9.312%	$271.5857	$271.59	$271.60	$271.60
Purchase #7	$33.96	5.402%	$35.7945	$35.79	$35.80	$35.80
7 purchase totals =	$1,010.16		$1,094.1630	$1,094.15	$1,094.20	$1,094.10