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	$203.45	9.526%	$222.8306	$222.83	$222.85	$222.80
Purchase #2	$137.70	4.673%	$144.1347	$144.13	$144.15	$144.10
Purchase #3	$86.97	12.815%	$98.1152	$98.12	$98.10	$98.10
Purchase #4	$120.25	13.701%	$136.7255	$136.73	$136.75	$136.70
Purchase #5	$205.57	7.685%	$221.3681	$221.37	$221.35	$221.40
Purchase #6	$25.37	10.136%	$27.9415	$27.94	$27.95	$27.90
Purchase #7	$48.90	11.473%	$54.5103	$54.51	$54.50	$54.50
7 purchase totals =	$828.21		$905.6259	$905.63	$905.65	$905.50