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	$170.81	5.577%	$180.3361	$180.34	$180.35	$180.30
Purchase #2	$67.54	7.216%	$72.4137	$72.41	$72.40	$72.40
Purchase #3	$155.42	5.615%	$164.1468	$164.15	$164.15	$164.10
Purchase #4	$69.35	11.751%	$77.4993	$77.50	$77.50	$77.50
Purchase #5	$78.78	11.394%	$87.7562	$87.76	$87.75	$87.80
Purchase #6	$119.30	11.271%	$132.7463	$132.75	$132.75	$132.70
Purchase #7	$161.78	11.709%	$180.7228	$180.72	$180.70	$180.70
7 purchase totals =	$822.98		$895.6212	$895.63	$895.60	$895.50