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	$130.73	7.296%	$140.2681	$140.27	$140.25	$140.30
Purchase #2	$202.58	10.272%	$223.389	$223.39	$223.40	$223.40
Purchase #3	$150.64	13.333%	$170.7248	$170.72	$170.70	$170.70
Purchase #4	$57.46	3.810%	$59.6492	$59.65	$59.65	$59.60
Purchase #5	$53.63	10.336%	$59.1732	$59.17	$59.15	$59.20
Purchase #6	$13.84	9.700%	$15.1825	$15.18	$15.20	$15.20
Purchase #7	$102.28	4.680%	$107.0667	$107.07	$107.05	$107.10
7 purchase totals =	$711.16		$775.4535	$775.45	$775.40	$775.50