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 $23.57   11.871%   $26.368   $26.37   $26.35   $26.40  
  Purchase #2 $95.73   10.435%   $105.7194   $105.72   $105.70   $105.70  
  Purchase #3 $69.98   5.462%   $73.8023   $73.80   $73.80   $73.80  
  Purchase #4 $98.91   3.671%   $102.541   $102.54   $102.55   $102.50  
  Purchase #5 $120.93   6.507%   $128.7989   $128.80   $128.80   $128.80  
  Purchase #6 $198.86   6.280%   $211.3484   $211.35   $211.35   $211.30  
  Purchase #7 $137.86   7.526%   $148.2353   $148.24   $148.25   $148.20  
  7 purchase totals = $745.84       $796.8133   $796.82   $796.80   $796.70