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	$48.68	11.295%	$54.1784	$54.18	$54.20	$54.20
Purchase #2	$147.45	5.798%	$155.9992	$156.00	$156.00	$156.00
Purchase #3	$105.31	12.345%	$118.3105	$118.31	$118.30	$118.30
Purchase #4	$55.26	7.624%	$59.473	$59.47	$59.45	$59.50
Purchase #5	$159.48	6.697%	$170.1604	$170.16	$170.15	$170.20
Purchase #6	$30.36	4.123%	$31.6117	$31.61	$31.60	$31.60
Purchase #7	$234.38	4.365%	$244.6107	$244.61	$244.60	$244.60
7 purchase totals =	$780.92		$834.3439	$834.34	$834.30	$834.40