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	$232.25	8.132%	$251.1366	$251.14	$251.15	$251.10
Purchase #2	$242.63	3.400%	$250.8794	$250.88	$250.90	$250.90
Purchase #3	$148.79	6.240%	$158.0745	$158.07	$158.05	$158.10
Purchase #4	$99.77	9.762%	$109.5095	$109.51	$109.50	$109.50
Purchase #5	$182.91	9.814%	$200.8608	$200.86	$200.85	$200.90
Purchase #6	$122.85	12.631%	$138.3672	$138.37	$138.35	$138.40
Purchase #7	$120.40	13.338%	$136.459	$136.46	$136.45	$136.50
7 purchase totals =	$1,149.60		$1,245.2870	$1,245.29	$1,245.25	$1,245.40