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	$37.49	13.399%	$42.5133	$42.51	$42.50	$42.50
Purchase #2	$83.83	12.785%	$94.5477	$94.55	$94.55	$94.50
Purchase #3	$111.93	7.549%	$120.3796	$120.38	$120.40	$120.40
Purchase #4	$176.46	11.359%	$196.5041	$196.50	$196.50	$196.50
Purchase #5	$10.94	10.862%	$12.1283	$12.13	$12.15	$12.10
Purchase #6	$162.38	6.832%	$173.4738	$173.47	$173.45	$173.50
Purchase #7	$112.73	5.340%	$118.7498	$118.75	$118.75	$118.70
7 purchase totals =	$695.76		$758.2966	$758.29	$758.30	$758.20