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	$77.83	8.705%	$84.6051	$84.61	$84.60	$84.60
Purchase #2	$177.67	7.384%	$190.7892	$190.79	$190.80	$190.80
Purchase #3	$37.61	4.808%	$39.4183	$39.42	$39.40	$39.40
Purchase #4	$162.66	13.331%	$184.3442	$184.34	$184.35	$184.30
Purchase #5	$90.71	10.385%	$100.1302	$100.13	$100.15	$100.10
Purchase #6	$62.48	8.538%	$67.8145	$67.81	$67.80	$67.80
Purchase #7	$221.56	6.697%	$236.3979	$236.40	$236.40	$236.40
7 purchase totals =	$830.52		$903.4994	$903.50	$903.50	$903.40