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	$158.61	7.377%	$170.3107	$170.31	$170.30	$170.30
Purchase #2	$37.83	12.182%	$42.4385	$42.44	$42.45	$42.40
Purchase #3	$43.44	11.270%	$48.3357	$48.34	$48.35	$48.30
Purchase #4	$114.39	8.260%	$123.8386	$123.84	$123.85	$123.80
Purchase #5	$91.49	7.344%	$98.209	$98.21	$98.20	$98.20
Purchase #6	$47.36	8.151%	$51.2203	$51.22	$51.20	$51.20
Purchase #7	$75.54	3.411%	$78.1167	$78.12	$78.10	$78.10
7 purchase totals =	$568.66		$612.4695	$612.48	$612.45	$612.30