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	$172.56	10.594%	$190.841	$190.84	$190.85	$190.80
Purchase #2	$249.71	9.434%	$273.2676	$273.27	$273.25	$273.30
Purchase #3	$156.73	5.194%	$164.8706	$164.87	$164.85	$164.90
Purchase #4	$136.83	6.654%	$145.9347	$145.93	$145.95	$145.90
Purchase #5	$60.64	8.169%	$65.5937	$65.59	$65.60	$65.60
Purchase #6	$228.94	7.239%	$245.513	$245.51	$245.50	$245.50
Purchase #7	$141.90	13.111%	$160.5045	$160.50	$160.50	$160.50
7 purchase totals =	$1,147.31		$1,246.5251	$1,246.51	$1,246.50	$1,246.50