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	$177.45	6.668%	$189.2824	$189.28	$189.30	$189.30
Purchase #2	$170.86	12.548%	$192.2995	$192.30	$192.30	$192.30
Purchase #3	$45.54	7.306%	$48.8672	$48.87	$48.85	$48.90
Purchase #4	$40.37	11.779%	$45.1252	$45.13	$45.15	$45.10
Purchase #5	$218.63	5.822%	$231.3586	$231.36	$231.35	$231.40
Purchase #6	$123.57	8.134%	$133.6212	$133.62	$133.60	$133.60
Purchase #7	$249.45	3.797%	$258.9216	$258.92	$258.90	$258.90
7 purchase totals =	$1,025.87		$1,099.4757	$1,099.48	$1,099.45	$1,099.50