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 $86.66   12.179%   $97.2143   $97.21   $97.20   $97.20  
  Purchase #2 $161.27   9.481%   $176.56   $176.56   $176.55   $176.60  
  Purchase #3 $145.92   4.783%   $152.8994   $152.90   $152.90   $152.90  
  Purchase #4 $47.27   5.533%   $49.8854   $49.89   $49.90   $49.90  
  Purchase #5 $25.71   3.793%   $26.6852   $26.69   $26.70   $26.70  
  Purchase #6 $242.40   9.303%   $264.9505   $264.95   $264.95   $265.00  
  Purchase #7 $87.63   13.458%   $99.4232   $99.42   $99.40   $99.40  
  7 purchase totals = $796.86       $867.6180   $867.62   $867.60   $867.70