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	$182.92	13.487%	$207.5904	$207.59	$207.60	$207.60
Purchase #2	$49.74	6.231%	$52.8393	$52.84	$52.85	$52.80
Purchase #3	$141.96	8.576%	$154.1345	$154.13	$154.15	$154.10
Purchase #4	$201.69	10.524%	$222.9159	$222.92	$222.90	$222.90
Purchase #5	$59.61	3.724%	$61.8299	$61.83	$61.85	$61.80
Purchase #6	$137.81	11.826%	$154.1074	$154.11	$154.10	$154.10
Purchase #7	$33.43	12.129%	$37.4847	$37.48	$37.50	$37.50
7 purchase totals =	$807.16		$890.9021	$890.90	$890.95	$890.80