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 $58.88   12.139%   $66.0274   $66.03   $66.05   $66.00  
  Purchase #2 $239.66   8.806%   $260.7645   $260.76   $260.75   $260.80  
  Purchase #3 $239.68   8.361%   $259.7196   $259.72   $259.70   $259.70  
  Purchase #4 $130.84   7.844%   $141.1031   $141.10   $141.10   $141.10  
  Purchase #5 $179.44   5.544%   $189.3882   $189.39   $189.40   $189.40  
  Purchase #6 $224.97   9.391%   $246.0969   $246.10   $246.10   $246.10  
  Purchase #7 $36.79   8.422%   $39.8885   $39.89   $39.90   $39.90  
  7 purchase totals = $1,110.26       $1,202.9882   $1,202.99   $1,203.00   $1,203.00