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 $126.49   11.143%   $140.5848   $140.58   $140.60   $140.60  
  Purchase #2 $199.98   9.374%   $218.7261   $218.73   $218.75   $218.70  
  Purchase #3 $76.45   8.183%   $82.7059   $82.71   $82.70   $82.70  
  Purchase #4 $161.72   3.801%   $167.867   $167.87   $167.85   $167.90  
  Purchase #5 $250.45   7.780%   $269.935   $269.94   $269.95   $269.90  
  Purchase #6 $180.66   7.327%   $193.897   $193.90   $193.90   $193.90  
  Purchase #7 $41.61   6.367%   $44.2593   $44.26   $44.25   $44.30  
  7 purchase totals = $1,037.36       $1,117.9751   $1,117.99   $1,118.00   $1,118.00