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 $56.66   3.356%   $58.5615   $58.56   $58.55   $58.60  
  Purchase #2 $221.60   6.517%   $236.0417   $236.04   $236.05   $236.00  
  Purchase #3 $30.61   13.510%   $34.7454   $34.75   $34.75   $34.70  
  Purchase #4 $127.83   11.187%   $142.1303   $142.13   $142.15   $142.10  
  Purchase #5 $177.69   4.175%   $185.1086   $185.11   $185.10   $185.10  
  Purchase #6 $191.40   12.361%   $215.059   $215.06   $215.05   $215.10  
  Purchase #7 $58.46   12.810%   $65.9487   $65.95   $65.95   $65.90  
  7 purchase totals = $864.25       $937.5952   $937.60   $937.60   $937.50