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	$10.96	12.442%	$12.3236	$12.32	$12.30	$12.30
Purchase #2	$99.29	12.502%	$111.7032	$111.70	$111.70	$111.70
Purchase #3	$124.27	13.855%	$141.4876	$141.49	$141.50	$141.50
Purchase #4	$52.38	8.155%	$56.6516	$56.65	$56.65	$56.70
Purchase #5	$148.91	13.591%	$169.1484	$169.15	$169.15	$169.10
Purchase #6	$180.78	12.581%	$203.5239	$203.52	$203.50	$203.50
Purchase #7	$132.51	9.786%	$145.4774	$145.48	$145.50	$145.50
7 purchase totals =	$749.10		$840.3157	$840.31	$840.30	$840.30