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	$76.27	12.103%	$85.501	$85.50	$85.50	$85.50
Purchase #2	$188.76	8.650%	$205.0877	$205.09	$205.10	$205.10
Purchase #3	$99.96	5.149%	$105.1069	$105.11	$105.10	$105.10
Purchase #4	$60.27	9.110%	$65.7606	$65.76	$65.75	$65.80
Purchase #5	$89.47	3.238%	$92.367	$92.37	$92.35	$92.40
Purchase #6	$140.76	12.139%	$157.8469	$157.85	$157.85	$157.80
Purchase #7	$143.72	12.867%	$162.2125	$162.21	$162.20	$162.20
7 purchase totals =	$799.21		$873.8826	$873.89	$873.85	$873.90