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	$30.48	11.327%	$33.9325	$33.93	$33.95	$33.90
Purchase #2	$19.85	7.202%	$21.2796	$21.28	$21.30	$21.30
Purchase #3	$152.48	5.145%	$160.3251	$160.33	$160.35	$160.30
Purchase #4	$49.65	12.308%	$55.7609	$55.76	$55.75	$55.80
Purchase #5	$58.88	13.616%	$66.8971	$66.90	$66.90	$66.90
Purchase #6	$39.79	13.849%	$45.3005	$45.30	$45.30	$45.30
Purchase #7	$124.56	11.555%	$138.9529	$138.95	$138.95	$139.00
7 purchase totals =	$475.69		$522.4486	$522.45	$522.50	$522.50