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	$136.47	10.433%	$150.7079	$150.71	$150.70	$150.70
Purchase #2	$155.98	13.255%	$176.6551	$176.66	$176.65	$176.70
Purchase #3	$162.62	8.200%	$175.9548	$175.95	$175.95	$176.00
Purchase #4	$95.66	4.361%	$99.8317	$99.83	$99.85	$99.80
Purchase #5	$80.55	13.626%	$91.5257	$91.53	$91.55	$91.50
Purchase #6	$104.40	12.727%	$117.687	$117.69	$117.70	$117.70
Purchase #7	$179.78	6.521%	$191.5035	$191.50	$191.50	$191.50
7 purchase totals =	$915.46		$1,003.8657	$1,003.87	$1,003.90	$1,003.90