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	$42.92	8.580%	$46.6025	$46.60	$46.60	$46.60
Purchase #2	$86.65	10.633%	$95.8635	$95.86	$95.85	$95.90
Purchase #3	$79.56	9.822%	$87.3744	$87.37	$87.35	$87.40
Purchase #4	$189.40	11.619%	$211.4064	$211.41	$211.40	$211.40
Purchase #5	$127.95	9.224%	$139.7521	$139.75	$139.75	$139.80
Purchase #6	$10.57	12.579%	$11.8996	$11.90	$11.90	$11.90
Purchase #7	$65.81	11.775%	$73.5591	$73.56	$73.55	$73.60
7 purchase totals =	$602.86		$666.4576	$666.45	$666.40	$666.60