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	$159.33	7.258%	$170.8942	$170.89	$170.90	$170.90
Purchase #2	$155.89	13.641%	$177.155	$177.16	$177.15	$177.20
Purchase #3	$141.42	8.643%	$153.6429	$153.64	$153.65	$153.60
Purchase #4	$192.66	4.533%	$201.3933	$201.39	$201.40	$201.40
Purchase #5	$40.47	5.402%	$42.6562	$42.66	$42.65	$42.70
Purchase #6	$228.96	6.497%	$243.8355	$243.84	$243.85	$243.80
Purchase #7	$83.43	8.582%	$90.59	$90.59	$90.60	$90.60
7 purchase totals =	$1,002.16		$1,080.1671	$1,080.17	$1,080.20	$1,080.20