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	$149.33	6.790%	$159.4695	$159.47	$159.45	$159.50
Purchase #2	$230.81	8.499%	$250.4265	$250.43	$250.45	$250.40
Purchase #3	$138.29	5.220%	$145.5087	$145.51	$145.50	$145.50
Purchase #4	$142.46	8.403%	$154.4309	$154.43	$154.45	$154.40
Purchase #5	$147.28	13.294%	$166.8594	$166.86	$166.85	$166.90
Purchase #6	$80.67	13.475%	$91.5403	$91.54	$91.55	$91.50
Purchase #7	$42.42	7.524%	$45.6117	$45.61	$45.60	$45.60
7 purchase totals =	$931.26		$1,013.8470	$1,013.85	$1,013.85	$1,013.80