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	$35.79	7.664%	$38.5329	$38.53	$38.55	$38.50
Purchase #2	$75.64	10.762%	$83.7804	$83.78	$83.80	$83.80
Purchase #3	$120.46	13.830%	$137.1196	$137.12	$137.10	$137.10
Purchase #4	$116.59	12.619%	$131.3025	$131.30	$131.30	$131.30
Purchase #5	$60.77	6.752%	$64.8732	$64.87	$64.85	$64.90
Purchase #6	$105.66	6.787%	$112.8311	$112.83	$112.85	$112.80
Purchase #7	$173.52	12.561%	$195.3158	$195.32	$195.30	$195.30
7 purchase totals =	$688.43		$763.7555	$763.75	$763.75	$763.70