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 $180.85   13.507%   $205.2774   $205.28   $205.30   $205.30  
  Purchase #2 $126.85   6.690%   $135.3363   $135.34   $135.35   $135.30  
  Purchase #3 $57.58   5.492%   $60.7423   $60.74   $60.75   $60.70  
  Purchase #4 $99.44   8.392%   $107.785   $107.79   $107.80   $107.80  
  Purchase #5 $193.75   6.122%   $205.6114   $205.61   $205.60   $205.60  
  Purchase #6 $191.34   3.675%   $198.3717   $198.37   $198.35   $198.40  
  Purchase #7 $52.72   3.618%   $54.6274   $54.63   $54.65   $54.60  
  7 purchase totals = $902.53       $967.7515   $967.76   $967.80   $967.70