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 $56.53   4.271%   $58.9444   $58.94   $58.95   $58.90  
  Purchase #2 $229.53   5.351%   $241.8122   $241.81   $241.80   $241.80  
  Purchase #3 $144.59   8.179%   $156.416   $156.42   $156.40   $156.40  
  Purchase #4 $238.31   9.254%   $260.3632   $260.36   $260.35   $260.40  
  Purchase #5 $188.98   6.688%   $201.619   $201.62   $201.60   $201.60  
  Purchase #6 $23.39   6.667%   $24.9494   $24.95   $24.95   $24.90  
  Purchase #7 $128.46   4.308%   $133.9941   $133.99   $134.00   $134.00  
  7 purchase totals = $1,009.79       $1,078.0983   $1,078.09   $1,078.05   $1,078.00