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	$166.72	11.310%	$185.576	$185.58	$185.60	$185.60
Purchase #2	$104.51	4.388%	$109.0959	$109.10	$109.10	$109.10
Purchase #3	$185.71	11.212%	$206.5318	$206.53	$206.55	$206.50
Purchase #4	$6.65	8.449%	$7.2119	$7.21	$7.20	$7.20
Purchase #5	$66.97	7.391%	$71.9198	$71.92	$71.90	$71.90
Purchase #6	$145.87	4.350%	$152.2153	$152.22	$152.20	$152.20
Purchase #7	$234.45	3.620%	$242.9371	$242.94	$242.95	$242.90
7 purchase totals =	$910.88		$975.4878	$975.50	$975.50	$975.40