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	$110.31	8.787%	$120.0029	$120.00	$120.00	$120.00
Purchase #2	$105.65	10.205%	$116.4316	$116.43	$116.45	$116.40
Purchase #3	$115.32	4.758%	$120.8069	$120.81	$120.80	$120.80
Purchase #4	$209.77	6.721%	$223.8686	$223.87	$223.85	$223.90
Purchase #5	$80.48	12.681%	$90.6857	$90.69	$90.70	$90.70
Purchase #6	$92.61	10.195%	$102.0516	$102.05	$102.05	$102.10
Purchase #7	$209.46	10.143%	$230.7055	$230.71	$230.70	$230.70
7 purchase totals =	$923.60		$1,004.5528	$1,004.56	$1,004.55	$1,004.60