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	$140.93	6.624%	$150.2652	$150.27	$150.25	$150.30
Purchase #2	$48.49	10.705%	$53.6809	$53.68	$53.70	$53.70
Purchase #3	$176.81	13.145%	$200.0517	$200.05	$200.05	$200.10
Purchase #4	$20.56	6.149%	$21.8242	$21.82	$21.80	$21.80
Purchase #5	$205.29	5.259%	$216.0862	$216.09	$216.10	$216.10
Purchase #6	$67.41	9.688%	$73.9407	$73.94	$73.95	$73.90
Purchase #7	$39.29	12.562%	$44.2256	$44.23	$44.25	$44.20
7 purchase totals =	$698.78		$760.0745	$760.08	$760.10	$760.10