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	$32.38	3.244%	$33.4304	$33.43	$33.45	$33.40
Purchase #2	$199.38	11.277%	$221.8641	$221.86	$221.85	$221.90
Purchase #3	$74.57	5.758%	$78.8637	$78.86	$78.85	$78.90
Purchase #4	$11.84	13.674%	$13.459	$13.46	$13.45	$13.50
Purchase #5	$48.96	3.481%	$50.6643	$50.66	$50.65	$50.70
Purchase #6	$126.63	13.526%	$143.758	$143.76	$143.75	$143.80
Purchase #7	$109.26	3.110%	$112.658	$112.66	$112.65	$112.70
7 purchase totals =	$603.02		$654.6975	$654.69	$654.65	$654.90