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 $24.42   6.666%   $26.0478   $26.05   $26.05   $26.00  
  Purchase #2 $159.80   8.614%   $173.5652   $173.57   $173.55   $173.60  
  Purchase #3 $97.38   13.169%   $110.204   $110.20   $110.20   $110.20  
  Purchase #4 $215.86   7.859%   $232.8244   $232.82   $232.80   $232.80  
  Purchase #5 $56.26   8.251%   $60.902   $60.90   $60.90   $60.90  
  Purchase #6 $83.75   11.725%   $93.5697   $93.57   $93.55   $93.60  
  Purchase #7 $109.72   12.615%   $123.5612   $123.56   $123.55   $123.60  
  7 purchase totals = $747.19       $820.6743   $820.67   $820.60   $820.70