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	$163.35	7.501%	$175.6029	$175.60	$175.60	$175.60
Purchase #2	$49.84	13.496%	$56.5664	$56.57	$56.55	$56.60
Purchase #3	$129.45	10.704%	$143.3063	$143.31	$143.30	$143.30
Purchase #4	$121.94	5.516%	$128.6662	$128.67	$128.65	$128.70
Purchase #5	$45.32	6.304%	$48.177	$48.18	$48.20	$48.20
Purchase #6	$55.54	6.237%	$59.004	$59.00	$59.00	$59.00
Purchase #7	$72.48	13.840%	$82.5112	$82.51	$82.50	$82.50
7 purchase totals =	$637.92		$693.8340	$693.84	$693.80	$693.90