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	$202.78	9.539%	$222.1232	$222.12	$222.10	$222.10
Purchase #2	$225.35	5.637%	$238.053	$238.05	$238.05	$238.10
Purchase #3	$130.74	10.365%	$144.2912	$144.29	$144.30	$144.30
Purchase #4	$25.63	11.123%	$28.4808	$28.48	$28.50	$28.50
Purchase #5	$41.68	11.392%	$46.4282	$46.43	$46.45	$46.40
Purchase #6	$136.87	3.459%	$141.6043	$141.60	$141.60	$141.60
Purchase #7	$120.95	3.300%	$124.9414	$124.94	$124.95	$124.90
7 purchase totals =	$884.00		$945.9221	$945.91	$945.95	$945.90