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 $189.69   13.663%   $215.6073   $215.61   $215.60   $215.60  
  Purchase #2 $146.28   10.197%   $161.1962   $161.20   $161.20   $161.20  
  Purchase #3 $41.83   3.746%   $43.397   $43.40   $43.40   $43.40  
  Purchase #4 $175.98   13.434%   $199.6212   $199.62   $199.60   $199.60  
  Purchase #5 $195.30   6.731%   $208.4456   $208.45   $208.45   $208.40  
  Purchase #6 $56.28   13.181%   $63.6983   $63.70   $63.70   $63.70  
  Purchase #7 $86.88   5.103%   $91.3135   $91.31   $91.30   $91.30  
  7 purchase totals = $892.24       $983.2791   $983.29   $983.25   $983.20