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	$37.88	10.582%	$41.8885	$41.89	$41.90	$41.90
Purchase #2	$139.65	4.268%	$145.6103	$145.61	$145.60	$145.60
Purchase #3	$230.59	6.557%	$245.7098	$245.71	$245.70	$245.70
Purchase #4	$188.55	11.724%	$210.6556	$210.66	$210.65	$210.70
Purchase #5	$10.69	10.342%	$11.7956	$11.80	$11.80	$11.80
Purchase #6	$9.50	12.865%	$10.7222	$10.72	$10.70	$10.70
Purchase #7	$85.97	4.468%	$89.8111	$89.81	$89.80	$89.80
7 purchase totals =	$702.83		$756.1931	$756.20	$756.15	$756.20