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	$134.74	6.418%	$143.3876	$143.39	$143.40	$143.40
Purchase #2	$146.73	9.412%	$160.5402	$160.54	$160.55	$160.50
Purchase #3	$30.34	12.628%	$34.1713	$34.17	$34.15	$34.20
Purchase #4	$219.97	12.290%	$247.0043	$247.00	$247.00	$247.00
Purchase #5	$198.61	13.648%	$225.7163	$225.72	$225.70	$225.70
Purchase #6	$39.73	13.602%	$45.1341	$45.13	$45.15	$45.10
Purchase #7	$105.82	3.448%	$109.4687	$109.47	$109.45	$109.50
7 purchase totals =	$875.94		$965.4225	$965.42	$965.40	$965.40