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	$239.70	3.138%	$247.2218	$247.22	$247.20	$247.20
Purchase #2	$77.31	7.681%	$83.2482	$83.25	$83.25	$83.20
Purchase #3	$225.31	7.576%	$242.3795	$242.38	$242.40	$242.40
Purchase #4	$191.35	4.738%	$200.4162	$200.42	$200.40	$200.40
Purchase #5	$223.92	12.162%	$251.1532	$251.15	$251.15	$251.20
Purchase #6	$227.94	12.138%	$255.6074	$255.61	$255.60	$255.60
Purchase #7	$51.43	8.665%	$55.8864	$55.89	$55.90	$55.90
7 purchase totals =	$1,236.96		$1,335.9127	$1,335.92	$1,335.90	$1,335.90