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	$37.51	13.502%	$42.5746	$42.57	$42.55	$42.60
Purchase #2	$125.38	8.276%	$135.7564	$135.76	$135.75	$135.80
Purchase #3	$186.81	6.767%	$199.4514	$199.45	$199.45	$199.50
Purchase #4	$233.39	3.218%	$240.9005	$240.90	$240.90	$240.90
Purchase #5	$64.52	9.843%	$70.8707	$70.87	$70.85	$70.90
Purchase #6	$200.52	10.873%	$222.3225	$222.32	$222.30	$222.30
Purchase #7	$120.30	4.695%	$125.9481	$125.95	$125.95	$125.90
7 purchase totals =	$968.43		$1,037.8242	$1,037.82	$1,037.75	$1,037.90