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	$88.69	3.401%	$91.7063	$91.71	$91.70	$91.70
Purchase #2	$82.42	7.522%	$88.6196	$88.62	$88.60	$88.60
Purchase #3	$117.71	13.767%	$133.9151	$133.92	$133.90	$133.90
Purchase #4	$106.80	12.365%	$120.0058	$120.01	$120.00	$120.00
Purchase #5	$70.48	8.613%	$76.5504	$76.55	$76.55	$76.60
Purchase #6	$29.89	12.112%	$33.5103	$33.51	$33.50	$33.50
Purchase #7	$18.81	7.863%	$20.289	$20.29	$20.30	$20.30
7 purchase totals =	$514.80		$564.5965	$564.61	$564.55	$564.60