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	$12.55	7.103%	$13.4414	$13.44	$13.45	$13.40
Purchase #2	$94.60	5.628%	$99.9241	$99.92	$99.90	$99.90
Purchase #3	$139.91	6.811%	$149.4393	$149.44	$149.45	$149.40
Purchase #4	$65.49	10.176%	$72.1543	$72.15	$72.15	$72.20
Purchase #5	$91.96	3.764%	$95.4214	$95.42	$95.40	$95.40
Purchase #6	$63.38	13.385%	$71.8634	$71.86	$71.85	$71.90
Purchase #7	$116.60	7.717%	$125.598	$125.60	$125.60	$125.60
7 purchase totals =	$584.49		$627.8419	$627.83	$627.80	$627.80