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	$93.61	13.609%	$106.3494	$106.35	$106.35	$106.30
Purchase #2	$242.64	5.729%	$256.5408	$256.54	$256.55	$256.50
Purchase #3	$116.91	12.284%	$131.2712	$131.27	$131.25	$131.30
Purchase #4	$157.90	7.181%	$169.2388	$169.24	$169.25	$169.20
Purchase #5	$35.94	7.248%	$38.5449	$38.54	$38.55	$38.50
Purchase #6	$49.42	13.806%	$56.2429	$56.24	$56.25	$56.20
Purchase #7	$139.57	5.194%	$146.8193	$146.82	$146.80	$146.80
7 purchase totals =	$835.99		$905.0073	$905.00	$905.00	$904.80