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 $23.38   13.494%   $26.5349   $26.53   $26.55   $26.50  
  Purchase #2 $152.93   13.741%   $173.9441   $173.94   $173.95   $173.90  
  Purchase #3 $8.95   10.144%   $9.8579   $9.86   $9.85   $9.90  
  Purchase #4 $15.56   13.757%   $17.7006   $17.70   $17.70   $17.70  
  Purchase #5 $213.95   4.351%   $223.259   $223.26   $223.25   $223.30  
  Purchase #6 $186.78   13.290%   $211.6031   $211.60   $211.60   $211.60  
  Purchase #7 $209.33   6.615%   $223.1772   $223.18   $223.20   $223.20  
  7 purchase totals = $810.88       $886.0768   $886.07   $886.10   $886.10