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 $54.63   10.432%   $60.329   $60.33   $60.35   $60.30  
  Purchase #2 $105.83   8.544%   $114.8721   $114.87   $114.85   $114.90  
  Purchase #3 $107.51   8.270%   $116.4011   $116.40   $116.40   $116.40  
  Purchase #4 $155.95   8.659%   $169.4537   $169.45   $169.45   $169.50  
  Purchase #5 $75.85   4.758%   $79.4589   $79.46   $79.45   $79.50  
  Purchase #6 $198.47   7.859%   $214.0678   $214.07   $214.05   $214.10  
  Purchase #7 $7.47   5.618%   $7.8897   $7.89   $7.90   $7.90  
  7 purchase totals = $705.71       $762.4723   $762.47   $762.45   $762.60