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	$43.97	6.106%	$46.6548	$46.65	$46.65	$46.70
Purchase #2	$108.59	10.185%	$119.6499	$119.65	$119.65	$119.60
Purchase #3	$134.73	4.765%	$141.1499	$141.15	$141.15	$141.10
Purchase #4	$135.89	3.118%	$140.1271	$140.13	$140.15	$140.10
Purchase #5	$128.27	5.568%	$135.4121	$135.41	$135.40	$135.40
Purchase #6	$78.85	7.808%	$85.0066	$85.01	$85.00	$85.00
Purchase #7	$204.61	8.743%	$222.4991	$222.50	$222.50	$222.50
7 purchase totals =	$834.91		$890.4995	$890.50	$890.50	$890.40