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 $91.26   13.568%   $103.6422   $103.64   $103.65   $103.60  
  Purchase #2 $76.76   8.598%   $83.3598   $83.36   $83.35   $83.40  
  Purchase #3 $242.80   6.319%   $258.1425   $258.14   $258.15   $258.10  
  Purchase #4 $211.92   9.433%   $231.9104   $231.91   $231.90   $231.90  
  Purchase #5 $94.73   8.601%   $102.8777   $102.88   $102.90   $102.90  
  Purchase #6 $49.79   12.859%   $56.1925   $56.19   $56.20   $56.20  
  Purchase #7 $118.90   10.302%   $131.1491   $131.15   $131.15   $131.10  
  7 purchase totals = $886.16       $967.2742   $967.27   $967.30   $967.20