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	$241.49	6.383%	$256.9043	$256.90	$256.90	$256.90
Purchase #2	$30.53	9.243%	$33.3519	$33.35	$33.35	$33.40
Purchase #3	$68.79	10.180%	$75.7928	$75.79	$75.80	$75.80
Purchase #4	$225.95	9.616%	$247.6774	$247.68	$247.70	$247.70
Purchase #5	$80.38	12.851%	$90.7096	$90.71	$90.70	$90.70
Purchase #6	$55.43	11.124%	$61.596	$61.60	$61.60	$61.60
Purchase #7	$93.86	6.702%	$100.1505	$100.15	$100.15	$100.20
7 purchase totals =	$796.43		$866.1825	$866.18	$866.20	$866.30