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 $54.72   8.527%   $59.386   $59.39   $59.40   $59.40  
  Purchase #2 $104.69   3.454%   $108.306   $108.31   $108.30   $108.30  
  Purchase #3 $175.40   5.476%   $185.0049   $185.00   $185.00   $185.00  
  Purchase #4 $50.69   11.664%   $56.6025   $56.60   $56.60   $56.60  
  Purchase #5 $27.37   8.120%   $29.5924   $29.59   $29.60   $29.60  
  Purchase #6 $197.88   8.733%   $215.1609   $215.16   $215.15   $215.20  
  Purchase #7 $216.61   9.379%   $236.9259   $236.93   $236.95   $236.90  
  7 purchase totals = $827.36       $890.9786   $890.98   $891.00   $891.00