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 $76.36   9.627%   $83.7112   $83.71   $83.70   $83.70  
  Purchase #2 $183.41   9.668%   $201.1421   $201.14   $201.15   $201.10  
  Purchase #3 $63.38   5.123%   $66.627   $66.63   $66.65   $66.60  
  Purchase #4 $241.34   7.190%   $258.6923   $258.69   $258.70   $258.70  
  Purchase #5 $6.56   7.165%   $7.03   $7.03   $7.05   $7.00  
  Purchase #6 $138.93   8.673%   $150.9794   $150.98   $151.00   $151.00  
  Purchase #7 $179.71   4.314%   $187.4627   $187.46   $187.45   $187.50  
  7 purchase totals = $889.69       $955.6447   $955.64   $955.70   $955.60