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	$49.43	12.256%	$55.4881	$55.49	$55.50	$55.50
Purchase #2	$223.61	6.534%	$238.2207	$238.22	$238.20	$238.20
Purchase #3	$36.54	7.438%	$39.2578	$39.26	$39.25	$39.30
Purchase #4	$149.72	10.130%	$164.8866	$164.89	$164.90	$164.90
Purchase #5	$211.58	7.700%	$227.8717	$227.87	$227.85	$227.90
Purchase #6	$89.59	7.810%	$96.587	$96.59	$96.60	$96.60
Purchase #7	$249.81	3.350%	$258.1786	$258.18	$258.20	$258.20
7 purchase totals =	$1,010.28		$1,080.4905	$1,080.50	$1,080.50	$1,080.60