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	$76.51	6.480%	$81.4678	$81.47	$81.45	$81.50
Purchase #2	$232.40	6.682%	$247.929	$247.93	$247.95	$247.90
Purchase #3	$216.91	10.821%	$240.3818	$240.38	$240.40	$240.40
Purchase #4	$50.31	8.183%	$54.4269	$54.43	$54.45	$54.40
Purchase #5	$53.74	11.386%	$59.8588	$59.86	$59.85	$59.90
Purchase #6	$65.54	4.363%	$68.3995	$68.40	$68.40	$68.40
Purchase #7	$10.94	4.474%	$11.4295	$11.43	$11.45	$11.40
7 purchase totals =	$706.35		$763.8933	$763.90	$763.95	$763.90