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 $81.69   13.686%   $92.8701   $92.87   $92.85   $92.90  
  Purchase #2 $114.33   10.158%   $125.9436   $125.94   $125.95   $125.90  
  Purchase #3 $156.94   5.682%   $165.8573   $165.86   $165.85   $165.90  
  Purchase #4 $149.94   4.130%   $156.1325   $156.13   $156.15   $156.10  
  Purchase #5 $218.32   13.163%   $247.0575   $247.06   $247.05   $247.10  
  Purchase #6 $225.95   13.601%   $256.6815   $256.68   $256.70   $256.70  
  Purchase #7 $173.61   8.112%   $187.6932   $187.69   $187.70   $187.70  
  7 purchase totals = $1,120.78       $1,232.2357   $1,232.23   $1,232.25   $1,232.30