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	$110.73	12.294%	$124.3431	$124.34	$124.35	$124.30
Purchase #2	$40.47	13.794%	$46.0524	$46.05	$46.05	$46.10
Purchase #3	$178.89	8.278%	$193.6985	$193.70	$193.70	$193.70
Purchase #4	$111.72	10.579%	$123.5389	$123.54	$123.55	$123.50
Purchase #5	$124.94	13.862%	$142.2592	$142.26	$142.25	$142.30
Purchase #6	$63.78	13.591%	$72.4483	$72.45	$72.45	$72.40
Purchase #7	$240.34	12.533%	$270.4618	$270.46	$270.45	$270.50
7 purchase totals =	$870.87		$972.8022	$972.80	$972.80	$972.80