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	$222.56	3.868%	$231.1686	$231.17	$231.15	$231.20
Purchase #2	$59.90	13.223%	$67.8206	$67.82	$67.80	$67.80
Purchase #3	$216.80	3.592%	$224.5875	$224.59	$224.60	$224.60
Purchase #4	$26.96	3.162%	$27.8125	$27.81	$27.80	$27.80
Purchase #5	$145.73	6.587%	$155.3292	$155.33	$155.35	$155.30
Purchase #6	$10.50	9.304%	$11.4769	$11.48	$11.50	$11.50
Purchase #7	$45.39	11.255%	$50.4986	$50.50	$50.50	$50.50
7 purchase totals =	$727.84		$768.6939	$768.70	$768.70	$768.70