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 $241.75   10.238%   $266.5004   $266.50   $266.50   $266.50  
  Purchase #2 $128.56   10.394%   $141.9225   $141.92   $141.90   $141.90  
  Purchase #3 $154.34   7.809%   $166.3924   $166.39   $166.40   $166.40  
  Purchase #4 $112.72   8.129%   $121.883   $121.88   $121.90   $121.90  
  Purchase #5 $159.91   6.698%   $170.6208   $170.62   $170.60   $170.60  
  Purchase #6 $87.67   5.366%   $92.3744   $92.37   $92.35   $92.40  
  Purchase #7 $157.91   4.474%   $164.9749   $164.97   $164.95   $165.00  
  7 purchase totals = $1,042.86       $1,124.6684   $1,124.65   $1,124.60   $1,124.70