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	$138.32	13.218%	$156.6031	$156.60	$156.60	$156.60
Purchase #2	$37.84	12.832%	$42.6956	$42.70	$42.70	$42.70
Purchase #3	$14.71	4.637%	$15.3921	$15.39	$15.40	$15.40
Purchase #4	$57.48	3.163%	$59.2981	$59.30	$59.30	$59.30
Purchase #5	$148.73	5.810%	$157.3712	$157.37	$157.35	$157.40
Purchase #6	$125.54	11.325%	$139.7574	$139.76	$139.75	$139.80
Purchase #7	$144.37	3.540%	$149.4807	$149.48	$149.50	$149.50
7 purchase totals =	$666.99		$720.5982	$720.60	$720.60	$720.70