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	$121.53	12.866%	$137.166	$137.17	$137.15	$137.20
Purchase #2	$148.68	12.630%	$167.4583	$167.46	$167.45	$167.50
Purchase #3	$72.38	13.113%	$81.8712	$81.87	$81.85	$81.90
Purchase #4	$98.48	13.296%	$111.5739	$111.57	$111.55	$111.60
Purchase #5	$232.25	5.798%	$245.7159	$245.72	$245.70	$245.70
Purchase #6	$152.25	8.606%	$165.3526	$165.35	$165.35	$165.40
Purchase #7	$45.37	7.407%	$48.7306	$48.73	$48.75	$48.70
7 purchase totals =	$870.94		$957.8685	$957.87	$957.80	$958.00