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	$158.48	6.835%	$169.3121	$169.31	$169.30	$169.30
Purchase #2	$65.28	13.383%	$74.0164	$74.02	$74.00	$74.00
Purchase #3	$25.57	9.531%	$28.0071	$28.01	$28.00	$28.00
Purchase #4	$43.83	3.143%	$45.2076	$45.21	$45.20	$45.20
Purchase #5	$79.69	13.404%	$90.3716	$90.37	$90.35	$90.40
Purchase #6	$29.81	3.398%	$30.8229	$30.82	$30.80	$30.80
Purchase #7	$147.77	12.583%	$166.3639	$166.36	$166.35	$166.40
7 purchase totals =	$550.43		$604.1016	$604.10	$604.00	$604.10