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	$84.97	12.111%	$95.2607	$95.26	$95.25	$95.30
Purchase #2	$247.48	5.494%	$261.0766	$261.08	$261.10	$261.10
Purchase #3	$211.66	13.412%	$240.0478	$240.05	$240.05	$240.00
Purchase #4	$96.58	8.296%	$104.5923	$104.59	$104.60	$104.60
Purchase #5	$90.72	10.345%	$100.105	$100.11	$100.10	$100.10
Purchase #6	$18.93	13.220%	$21.4325	$21.43	$21.45	$21.40
Purchase #7	$63.47	3.338%	$65.5886	$65.59	$65.60	$65.60
7 purchase totals =	$813.81		$888.1035	$888.11	$888.15	$888.10