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	$155.61	5.721%	$164.5124	$164.51	$164.50	$164.50
Purchase #2	$27.89	3.513%	$28.8698	$28.87	$28.85	$28.90
Purchase #3	$174.58	8.236%	$188.9584	$188.96	$188.95	$189.00
Purchase #4	$240.78	3.624%	$249.5059	$249.51	$249.50	$249.50
Purchase #5	$146.69	12.382%	$164.8532	$164.85	$164.85	$164.90
Purchase #6	$173.29	6.843%	$185.1482	$185.15	$185.15	$185.10
Purchase #7	$207.50	11.366%	$231.0845	$231.08	$231.10	$231.10
7 purchase totals =	$1,126.34		$1,212.9324	$1,212.93	$1,212.90	$1,213.00