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	$125.50	9.479%	$137.3961	$137.40	$137.40	$137.40
Purchase #2	$199.35	11.814%	$222.9012	$222.90	$222.90	$222.90
Purchase #3	$94.44	8.501%	$102.4683	$102.47	$102.45	$102.50
Purchase #4	$18.39	12.675%	$20.7209	$20.72	$20.70	$20.70
Purchase #5	$74.91	4.370%	$78.1836	$78.18	$78.20	$78.20
Purchase #6	$131.41	5.354%	$138.4457	$138.45	$138.45	$138.40
Purchase #7	$20.70	5.729%	$21.8859	$21.89	$21.90	$21.90
7 purchase totals =	$664.70		$722.0017	$722.01	$722.00	$722.00