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	$112.94	6.791%	$120.6098	$120.61	$120.60	$120.60
Purchase #2	$78.89	8.576%	$85.6556	$85.66	$85.65	$85.70
Purchase #3	$121.38	10.284%	$133.8627	$133.86	$133.85	$133.90
Purchase #4	$81.47	5.567%	$86.0054	$86.01	$86.00	$86.00
Purchase #5	$195.30	12.472%	$219.6578	$219.66	$219.65	$219.70
Purchase #6	$212.74	9.107%	$232.1142	$232.11	$232.10	$232.10
Purchase #7	$195.83	13.513%	$222.2925	$222.29	$222.30	$222.30
7 purchase totals =	$998.55		$1,100.1980	$1,100.20	$1,100.15	$1,100.30