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	$236.70	8.246%	$256.2183	$256.22	$256.20	$256.20
Purchase #2	$196.98	3.213%	$203.309	$203.31	$203.30	$203.30
Purchase #3	$127.26	10.865%	$141.0868	$141.09	$141.10	$141.10
Purchase #4	$83.83	7.113%	$89.7928	$89.79	$89.80	$89.80
Purchase #5	$59.96	13.283%	$67.9245	$67.92	$67.90	$67.90
Purchase #6	$207.59	5.322%	$218.6379	$218.64	$218.65	$218.60
Purchase #7	$224.90	10.482%	$248.474	$248.47	$248.45	$248.50
7 purchase totals =	$1,137.22		$1,225.4433	$1,225.44	$1,225.40	$1,225.40