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	$135.27	10.322%	$149.2326	$149.23	$149.25	$149.20
Purchase #2	$98.77	13.215%	$111.8225	$111.82	$111.80	$111.80
Purchase #3	$51.94	7.824%	$56.0038	$56.00	$56.00	$56.00
Purchase #4	$33.42	5.218%	$35.1639	$35.16	$35.15	$35.20
Purchase #5	$78.84	13.170%	$89.2232	$89.22	$89.20	$89.20
Purchase #6	$192.52	13.410%	$218.3369	$218.34	$218.35	$218.30
Purchase #7	$246.87	12.357%	$277.3757	$277.38	$277.40	$277.40
7 purchase totals =	$837.63		$937.1586	$937.15	$937.15	$937.10