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	$141.68	10.304%	$156.2787	$156.28	$156.30	$156.30
Purchase #2	$48.59	12.834%	$54.826	$54.83	$54.85	$54.80
Purchase #3	$123.76	6.584%	$131.9084	$131.91	$131.90	$131.90
Purchase #4	$119.32	8.529%	$129.4968	$129.50	$129.50	$129.50
Purchase #5	$130.65	6.648%	$139.3356	$139.34	$139.35	$139.30
Purchase #6	$21.54	12.173%	$24.1621	$24.16	$24.15	$24.20
Purchase #7	$221.61	13.204%	$250.8714	$250.87	$250.85	$250.90
7 purchase totals =	$807.15		$886.8790	$886.89	$886.90	$886.90