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	$197.92	12.627%	$222.9114	$222.91	$222.90	$222.90
Purchase #2	$92.34	13.584%	$104.8835	$104.88	$104.90	$104.90
Purchase #3	$109.58	12.131%	$122.8731	$122.87	$122.85	$122.90
Purchase #4	$45.28	9.281%	$49.4824	$49.48	$49.50	$49.50
Purchase #5	$190.63	11.209%	$211.9977	$212.00	$212.00	$212.00
Purchase #6	$139.52	8.745%	$151.721	$151.72	$151.70	$151.70
Purchase #7	$124.89	9.585%	$136.8607	$136.86	$136.85	$136.90
7 purchase totals =	$900.16		$1,000.7298	$1,000.72	$1,000.70	$1,000.80