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 $60.47   12.175%   $67.8322   $67.83   $67.85   $67.80  
  Purchase #2 $219.94   7.433%   $236.2881   $236.29   $236.30   $236.30  
  Purchase #3 $205.80   7.201%   $220.6197   $220.62   $220.60   $220.60  
  Purchase #4 $141.66   3.600%   $146.7598   $146.76   $146.75   $146.80  
  Purchase #5 $117.82   3.189%   $121.5773   $121.58   $121.60   $121.60  
  Purchase #6 $136.89   6.871%   $146.2957   $146.30   $146.30   $146.30  
  Purchase #7 $165.58   5.228%   $174.2365   $174.24   $174.25   $174.20  
  7 purchase totals = $1,048.16       $1,113.6093   $1,113.62   $1,113.65   $1,113.60