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	$250.51	12.681%	$282.2772	$282.28	$282.30	$282.30
Purchase #2	$40.38	9.607%	$44.2593	$44.26	$44.25	$44.30
Purchase #3	$55.63	13.668%	$63.2335	$63.23	$63.25	$63.20
Purchase #4	$205.73	8.307%	$222.82	$222.82	$222.80	$222.80
Purchase #5	$136.69	11.112%	$151.879	$151.88	$151.90	$151.90
Purchase #6	$69.54	7.321%	$74.631	$74.63	$74.65	$74.60
Purchase #7	$55.68	7.213%	$59.6962	$59.70	$59.70	$59.70
7 purchase totals =	$814.16		$898.7962	$898.80	$898.85	$898.80