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	$34.46	13.324%	$39.0515	$39.05	$39.05	$39.10
Purchase #2	$45.70	6.385%	$48.6179	$48.62	$48.60	$48.60
Purchase #3	$144.97	8.243%	$156.9199	$156.92	$156.90	$156.90
Purchase #4	$46.96	9.802%	$51.563	$51.56	$51.55	$51.60
Purchase #5	$134.36	10.731%	$148.7782	$148.78	$148.80	$148.80
Purchase #6	$20.53	9.646%	$22.5103	$22.51	$22.50	$22.50
Purchase #7	$113.35	12.317%	$127.3113	$127.31	$127.30	$127.30
7 purchase totals =	$540.33		$594.7521	$594.75	$594.70	$594.80