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 $67.58   5.312%   $71.1698   $71.17   $71.15   $71.20  
  Purchase #2 $157.35   9.798%   $172.7672   $172.77   $172.75   $172.80  
  Purchase #3 $180.59   10.156%   $198.9307   $198.93   $198.95   $198.90  
  Purchase #4 $74.47   3.301%   $76.9283   $76.93   $76.95   $76.90  
  Purchase #5 $26.88   13.272%   $30.4475   $30.45   $30.45   $30.40  
  Purchase #6 $26.27   9.658%   $28.8072   $28.81   $28.80   $28.80  
  Purchase #7 $20.36   12.599%   $22.9252   $22.93   $22.95   $22.90  
  7 purchase totals = $553.50       $601.9759   $601.99   $602.00   $601.90