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	$36.59	10.334%	$40.3712	$40.37	$40.35	$40.40
Purchase #2	$129.38	8.856%	$140.8379	$140.84	$140.85	$140.80
Purchase #3	$137.45	13.180%	$155.5659	$155.57	$155.55	$155.60
Purchase #4	$53.81	12.360%	$60.4609	$60.46	$60.45	$60.50
Purchase #5	$76.49	11.311%	$85.1418	$85.14	$85.15	$85.10
Purchase #6	$96.85	3.137%	$99.8882	$99.89	$99.90	$99.90
Purchase #7	$181.56	4.871%	$190.4038	$190.40	$190.40	$190.40
7 purchase totals =	$712.13		$772.6697	$772.67	$772.65	$772.70