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	$130.32	12.149%	$146.1526	$146.15	$146.15	$146.20
Purchase #2	$53.38	8.160%	$57.7358	$57.74	$57.75	$57.70
Purchase #3	$19.58	7.637%	$21.0753	$21.08	$21.10	$21.10
Purchase #4	$9.80	8.375%	$10.6208	$10.62	$10.60	$10.60
Purchase #5	$27.63	4.336%	$28.828	$28.83	$28.85	$28.80
Purchase #6	$80.46	4.266%	$83.8924	$83.89	$83.90	$83.90
Purchase #7	$238.44	3.807%	$247.5174	$247.52	$247.50	$247.50
7 purchase totals =	$559.61		$595.8223	$595.83	$595.85	$595.80