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	$9.55	6.362%	$10.1576	$10.16	$10.15	$10.20
Purchase #2	$141.41	11.399%	$157.5293	$157.53	$157.55	$157.50
Purchase #3	$173.34	10.854%	$192.1543	$192.15	$192.15	$192.20
Purchase #4	$52.31	9.755%	$57.4128	$57.41	$57.40	$57.40
Purchase #5	$168.41	4.186%	$175.4596	$175.46	$175.45	$175.50
Purchase #6	$18.29	3.466%	$18.9239	$18.92	$18.90	$18.90
Purchase #7	$196.44	13.214%	$222.3976	$222.40	$222.40	$222.40
7 purchase totals =	$759.75		$834.0351	$834.03	$834.00	$834.10