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	$36.69	9.467%	$40.1634	$40.16	$40.15	$40.20
Purchase #2	$58.50	13.813%	$66.5806	$66.58	$66.60	$66.60
Purchase #3	$205.85	8.152%	$222.6309	$222.63	$222.65	$222.60
Purchase #4	$41.55	7.872%	$44.8208	$44.82	$44.80	$44.80
Purchase #5	$214.73	11.362%	$239.1276	$239.13	$239.15	$239.10
Purchase #6	$250.85	6.695%	$267.6444	$267.64	$267.65	$267.60
Purchase #7	$186.35	9.816%	$204.6421	$204.64	$204.65	$204.60
7 purchase totals =	$994.52		$1,085.6098	$1,085.60	$1,085.65	$1,085.50