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 $68.35   8.116%   $73.8973   $73.90   $73.90   $73.90  
  Purchase #2 $240.58   4.775%   $252.0677   $252.07   $252.05   $252.10  
  Purchase #3 $87.37   13.682%   $99.324   $99.32   $99.30   $99.30  
  Purchase #4 $159.95   9.175%   $174.6254   $174.63   $174.65   $174.60  
  Purchase #5 $131.86   12.458%   $148.2871   $148.29   $148.30   $148.30  
  Purchase #6 $164.85   5.821%   $174.4459   $174.45   $174.45   $174.40  
  Purchase #7 $21.66   9.681%   $23.7569   $23.76   $23.75   $23.80  
  7 purchase totals = $874.62       $946.4043   $946.42   $946.40   $946.40