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	$59.63	10.811%	$66.0766	$66.08	$66.10	$66.10
Purchase #2	$197.55	3.650%	$204.7606	$204.76	$204.75	$204.80
Purchase #3	$99.34	11.650%	$110.9131	$110.91	$110.90	$110.90
Purchase #4	$75.37	11.259%	$83.8559	$83.86	$83.85	$83.90
Purchase #5	$9.35	7.293%	$10.0319	$10.03	$10.05	$10.00
Purchase #6	$104.37	7.207%	$111.8919	$111.89	$111.90	$111.90
Purchase #7	$20.49	5.152%	$21.5456	$21.55	$21.55	$21.50
7 purchase totals =	$566.10		$609.0756	$609.08	$609.10	$609.10