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	$16.31	11.502%	$18.186	$18.19	$18.20	$18.20
Purchase #2	$75.89	6.152%	$80.5588	$80.56	$80.55	$80.60
Purchase #3	$11.50	8.850%	$12.5178	$12.52	$12.50	$12.50
Purchase #4	$126.85	7.491%	$136.3523	$136.35	$136.35	$136.40
Purchase #5	$73.71	6.517%	$78.5137	$78.51	$78.50	$78.50
Purchase #6	$23.41	7.807%	$25.2376	$25.24	$25.25	$25.20
Purchase #7	$95.94	5.464%	$101.1822	$101.18	$101.20	$101.20
7 purchase totals =	$423.61		$452.5484	$452.55	$452.55	$452.60