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	$161.51	4.318%	$168.484	$168.48	$168.50	$168.50
Purchase #2	$103.66	5.650%	$109.5168	$109.52	$109.50	$109.50
Purchase #3	$75.94	9.517%	$83.1672	$83.17	$83.15	$83.20
Purchase #4	$77.60	11.167%	$86.2656	$86.27	$86.25	$86.30
Purchase #5	$19.54	8.281%	$21.1581	$21.16	$21.15	$21.20
Purchase #6	$190.41	3.871%	$197.7808	$197.78	$197.80	$197.80
Purchase #7	$231.66	5.170%	$243.6368	$243.64	$243.65	$243.60
7 purchase totals =	$860.32		$910.0093	$910.02	$910.00	$910.10