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	$49.40	13.828%	$56.231	$56.23	$56.25	$56.20
Purchase #2	$243.29	5.626%	$256.9775	$256.98	$257.00	$257.00
Purchase #3	$91.38	8.788%	$99.4105	$99.41	$99.40	$99.40
Purchase #4	$85.40	13.478%	$96.9102	$96.91	$96.90	$96.90
Purchase #5	$246.63	4.164%	$256.8997	$256.90	$256.90	$256.90
Purchase #6	$91.53	13.162%	$103.5772	$103.58	$103.60	$103.60
Purchase #7	$120.34	4.595%	$125.8696	$125.87	$125.85	$125.90
7 purchase totals =	$927.97		$995.8757	$995.88	$995.90	$995.90