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	$36.41	7.473%	$39.1309	$39.13	$39.15	$39.10
Purchase #2	$59.50	13.236%	$67.3754	$67.38	$67.40	$67.40
Purchase #3	$84.54	9.640%	$92.6897	$92.69	$92.70	$92.70
Purchase #4	$109.64	13.345%	$124.2715	$124.27	$124.25	$124.30
Purchase #5	$48.80	3.470%	$50.4934	$50.49	$50.50	$50.50
Purchase #6	$152.81	5.190%	$160.7408	$160.74	$160.75	$160.70
Purchase #7	$201.72	10.872%	$223.651	$223.65	$223.65	$223.70
7 purchase totals =	$693.42		$758.3527	$758.35	$758.40	$758.40