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	$171.78	11.868%	$192.1669	$192.17	$192.15	$192.20
Purchase #2	$80.84	13.732%	$91.9409	$91.94	$91.95	$91.90
Purchase #3	$66.66	8.237%	$72.1508	$72.15	$72.15	$72.20
Purchase #4	$109.27	13.341%	$123.8477	$123.85	$123.85	$123.80
Purchase #5	$221.35	8.298%	$239.7176	$239.72	$239.70	$239.70
Purchase #6	$142.71	4.229%	$148.7452	$148.75	$148.75	$148.70
Purchase #7	$122.80	9.853%	$134.8995	$134.90	$134.90	$134.90
7 purchase totals =	$915.41		$1,003.4686	$1,003.48	$1,003.45	$1,003.40