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	$19.60	10.271%	$21.6131	$21.61	$21.60	$21.60
Purchase #2	$169.36	6.222%	$179.8976	$179.90	$179.90	$179.90
Purchase #3	$159.29	6.484%	$169.6184	$169.62	$169.60	$169.60
Purchase #4	$226.92	9.745%	$249.0334	$249.03	$249.05	$249.00
Purchase #5	$35.51	6.699%	$37.8888	$37.89	$37.90	$37.90
Purchase #6	$123.27	11.673%	$137.6593	$137.66	$137.65	$137.70
Purchase #7	$155.30	9.196%	$169.5814	$169.58	$169.60	$169.60
7 purchase totals =	$889.25		$965.2920	$965.29	$965.30	$965.30