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	$23.78	6.208%	$25.2563	$25.26	$25.25	$25.30
Purchase #2	$250.43	5.642%	$264.5593	$264.56	$264.55	$264.60
Purchase #3	$233.57	9.357%	$255.4251	$255.43	$255.45	$255.40
Purchase #4	$36.64	11.754%	$40.9467	$40.95	$40.95	$40.90
Purchase #5	$25.62	5.427%	$27.0104	$27.01	$27.00	$27.00
Purchase #6	$25.61	7.598%	$27.5558	$27.56	$27.55	$27.60
Purchase #7	$73.59	13.781%	$83.7314	$83.73	$83.75	$83.70
7 purchase totals =	$669.24		$724.4850	$724.50	$724.50	$724.50