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	$242.77	13.369%	$275.2259	$275.23	$275.25	$275.20
Purchase #2	$148.53	13.456%	$168.5162	$168.52	$168.50	$168.50
Purchase #3	$206.33	13.707%	$234.6117	$234.61	$234.60	$234.60
Purchase #4	$216.58	11.473%	$241.4282	$241.43	$241.45	$241.40
Purchase #5	$53.86	11.380%	$59.9893	$59.99	$60.00	$60.00
Purchase #6	$151.32	8.695%	$164.4773	$164.48	$164.50	$164.50
Purchase #7	$191.25	12.203%	$214.5882	$214.59	$214.60	$214.60
7 purchase totals =	$1,210.64		$1,358.8368	$1,358.85	$1,358.90	$1,358.80