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	$82.35	3.487%	$85.2215	$85.22	$85.20	$85.20
Purchase #2	$205.70	8.524%	$223.2339	$223.23	$223.25	$223.20
Purchase #3	$137.82	6.204%	$146.3704	$146.37	$146.35	$146.40
Purchase #4	$38.77	13.539%	$44.0191	$44.02	$44.00	$44.00
Purchase #5	$47.56	6.185%	$50.5016	$50.50	$50.50	$50.50
Purchase #6	$156.31	9.186%	$170.6686	$170.67	$170.65	$170.70
Purchase #7	$103.58	12.470%	$116.4964	$116.50	$116.50	$116.50
7 purchase totals =	$772.09		$836.5115	$836.51	$836.45	$836.50