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	$216.54	12.451%	$243.5014	$243.50	$243.50	$243.50
Purchase #2	$152.43	5.106%	$160.2131	$160.21	$160.20	$160.20
Purchase #3	$126.80	9.248%	$138.5265	$138.53	$138.55	$138.50
Purchase #4	$68.27	6.131%	$72.4556	$72.46	$72.45	$72.50
Purchase #5	$138.98	5.120%	$146.0958	$146.10	$146.10	$146.10
Purchase #6	$198.71	10.257%	$219.0917	$219.09	$219.10	$219.10
Purchase #7	$52.43	13.223%	$59.3628	$59.36	$59.35	$59.40
7 purchase totals =	$954.16		$1,039.2469	$1,039.25	$1,039.25	$1,039.30