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	$11.31	7.266%	$12.1318	$12.13	$12.15	$12.10
Purchase #2	$67.97	6.389%	$72.3126	$72.31	$72.30	$72.30
Purchase #3	$192.92	13.336%	$218.6478	$218.65	$218.65	$218.60
Purchase #4	$121.85	8.420%	$132.1098	$132.11	$132.10	$132.10
Purchase #5	$217.77	3.399%	$225.172	$225.17	$225.15	$225.20
Purchase #6	$166.57	9.447%	$182.3059	$182.31	$182.30	$182.30
Purchase #7	$38.44	5.294%	$40.475	$40.48	$40.50	$40.50
7 purchase totals =	$816.83		$883.1549	$883.16	$883.15	$883.10