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	$124.71	13.290%	$141.284	$141.28	$141.30	$141.30
Purchase #2	$42.99	5.790%	$45.4791	$45.48	$45.50	$45.50
Purchase #3	$154.71	7.240%	$165.911	$165.91	$165.90	$165.90
Purchase #4	$36.49	11.538%	$40.7002	$40.70	$40.70	$40.70
Purchase #5	$27.54	13.578%	$31.2794	$31.28	$31.30	$31.30
Purchase #6	$238.88	8.499%	$259.1824	$259.18	$259.20	$259.20
Purchase #7	$168.67	9.578%	$184.8252	$184.83	$184.85	$184.80
7 purchase totals =	$793.99		$868.6613	$868.66	$868.75	$868.70