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 $126.62   5.715%   $133.8563   $133.86   $133.85   $133.90  
  Purchase #2 $63.49   4.295%   $66.2169   $66.22   $66.20   $66.20  
  Purchase #3 $116.81   7.592%   $125.6782   $125.68   $125.70   $125.70  
  Purchase #4 $198.62   7.687%   $213.8879   $213.89   $213.90   $213.90  
  Purchase #5 $66.92   4.547%   $69.9629   $69.96   $69.95   $70.00  
  Purchase #6 $250.39   12.487%   $281.6562   $281.66   $281.65   $281.70  
  Purchase #7 $61.39   13.610%   $69.7452   $69.75   $69.75   $69.70  
  7 purchase totals = $884.24       $961.0036   $961.02   $961.00   $961.10