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	$233.97	6.654%	$249.5384	$249.54	$249.55	$249.50
Purchase #2	$170.33	8.331%	$184.5202	$184.52	$184.50	$184.50
Purchase #3	$203.74	8.725%	$221.5163	$221.52	$221.50	$221.50
Purchase #4	$147.28	3.125%	$151.8825	$151.88	$151.90	$151.90
Purchase #5	$212.60	8.789%	$231.2854	$231.29	$231.30	$231.30
Purchase #6	$35.40	13.275%	$40.0994	$40.10	$40.10	$40.10
Purchase #7	$225.74	12.717%	$254.4474	$254.45	$254.45	$254.40
7 purchase totals =	$1,229.06		$1,333.2896	$1,333.30	$1,333.30	$1,333.20