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	$95.74	13.754%	$108.9081	$108.91	$108.90	$108.90
Purchase #2	$74.63	12.478%	$83.9423	$83.94	$83.95	$83.90
Purchase #3	$90.80	10.270%	$100.1252	$100.13	$100.15	$100.10
Purchase #4	$39.90	6.658%	$42.5565	$42.56	$42.55	$42.60
Purchase #5	$199.51	6.264%	$212.0073	$212.01	$212.00	$212.00
Purchase #6	$198.86	13.521%	$225.7479	$225.75	$225.75	$225.70
Purchase #7	$57.66	8.477%	$62.5478	$62.55	$62.55	$62.50
7 purchase totals =	$757.10		$835.8351	$835.85	$835.85	$835.70