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	$108.33	10.214%	$119.3948	$119.39	$119.40	$119.40
Purchase #2	$160.94	5.858%	$170.3679	$170.37	$170.35	$170.40
Purchase #3	$129.81	9.305%	$141.8888	$141.89	$141.90	$141.90
Purchase #4	$144.69	6.361%	$153.8937	$153.89	$153.90	$153.90
Purchase #5	$151.53	9.126%	$165.3586	$165.36	$165.35	$165.40
Purchase #6	$209.98	11.325%	$233.7602	$233.76	$233.75	$233.80
Purchase #7	$64.86	11.778%	$72.4992	$72.50	$72.50	$72.50
7 purchase totals =	$970.14		$1,057.1632	$1,057.16	$1,057.15	$1,057.30