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	$175.88	5.116%	$184.878	$184.88	$184.90	$184.90
Purchase #2	$220.85	10.629%	$244.3241	$244.32	$244.30	$244.30
Purchase #3	$149.29	12.590%	$168.0856	$168.09	$168.10	$168.10
Purchase #4	$83.74	12.386%	$94.112	$94.11	$94.10	$94.10
Purchase #5	$227.54	13.770%	$258.8723	$258.87	$258.85	$258.90
Purchase #6	$107.67	3.372%	$111.3006	$111.30	$111.30	$111.30
Purchase #7	$208.60	6.741%	$222.6617	$222.66	$222.65	$222.70
7 purchase totals =	$1,173.57		$1,284.2343	$1,284.23	$1,284.20	$1,284.30