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 $24.53   8.226%   $26.5478   $26.55   $26.55   $26.50  
  Purchase #2 $109.62   9.168%   $119.67   $119.67   $119.65   $119.70  
  Purchase #3 $123.87   13.786%   $140.9467   $140.95   $140.95   $140.90  
  Purchase #4 $185.31   5.151%   $194.8553   $194.86   $194.85   $194.90  
  Purchase #5 $203.85   12.161%   $228.6402   $228.64   $228.65   $228.60  
  Purchase #6 $16.85   12.762%   $19.0004   $19.00   $19.00   $19.00  
  Purchase #7 $49.83   13.124%   $56.3697   $56.37   $56.35   $56.40  
  7 purchase totals = $713.86       $786.0301   $786.04   $786.00   $786.00