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	$108.29	13.592%	$123.0088	$123.01	$123.00	$123.00
Purchase #2	$242.48	13.300%	$274.7298	$274.73	$274.75	$274.70
Purchase #3	$215.71	4.854%	$226.1806	$226.18	$226.20	$226.20
Purchase #4	$96.37	9.362%	$105.3922	$105.39	$105.40	$105.40
Purchase #5	$94.78	11.717%	$105.8854	$105.89	$105.90	$105.90
Purchase #6	$170.72	5.539%	$180.1762	$180.18	$180.20	$180.20
Purchase #7	$102.70	5.520%	$108.369	$108.37	$108.35	$108.40
7 purchase totals =	$1,031.05		$1,123.7420	$1,123.75	$1,123.80	$1,123.80