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	$59.27	12.811%	$66.8631	$66.86	$66.85	$66.90
Purchase #2	$139.51	12.756%	$157.3059	$157.31	$157.30	$157.30
Purchase #3	$235.31	6.494%	$250.591	$250.59	$250.60	$250.60
Purchase #4	$20.85	10.814%	$23.1047	$23.10	$23.10	$23.10
Purchase #5	$32.95	13.416%	$37.3706	$37.37	$37.35	$37.40
Purchase #6	$28.42	11.149%	$31.5885	$31.59	$31.60	$31.60
Purchase #7	$79.60	11.291%	$88.5876	$88.59	$88.60	$88.60
7 purchase totals =	$595.91		$655.4114	$655.41	$655.40	$655.50