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	$150.30	10.120%	$165.5104	$165.51	$165.50	$165.50
Purchase #2	$99.57	5.556%	$105.1021	$105.10	$105.10	$105.10
Purchase #3	$206.35	11.389%	$229.8512	$229.85	$229.85	$229.90
Purchase #4	$209.86	6.171%	$222.8105	$222.81	$222.80	$222.80
Purchase #5	$33.82	13.348%	$38.3343	$38.33	$38.35	$38.30
Purchase #6	$150.75	6.374%	$160.3588	$160.36	$160.35	$160.40
Purchase #7	$23.92	5.124%	$25.1457	$25.15	$25.15	$25.10
7 purchase totals =	$874.57		$947.1130	$947.11	$947.10	$947.10