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	$210.55	4.296%	$219.5952	$219.60	$219.60	$219.60
Purchase #2	$66.83	6.873%	$71.4232	$71.42	$71.40	$71.40
Purchase #3	$81.44	10.200%	$89.7469	$89.75	$89.75	$89.70
Purchase #4	$50.58	13.267%	$57.2904	$57.29	$57.30	$57.30
Purchase #5	$36.42	12.179%	$40.8556	$40.86	$40.85	$40.90
Purchase #6	$116.51	3.127%	$120.1533	$120.15	$120.15	$120.20
Purchase #7	$9.73	4.452%	$10.1632	$10.16	$10.15	$10.20
7 purchase totals =	$572.06		$609.2278	$609.23	$609.20	$609.30