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 $232.58   13.341%   $263.6085   $263.61   $263.60   $263.60  
  Purchase #2 $245.95   6.791%   $262.6525   $262.65   $262.65   $262.70  
  Purchase #3 $130.62   10.838%   $144.7766   $144.78   $144.80   $144.80  
  Purchase #4 $184.82   3.686%   $191.6325   $191.63   $191.65   $191.60  
  Purchase #5 $25.26   5.521%   $26.6546   $26.65   $26.65   $26.70  
  Purchase #6 $244.85   12.677%   $275.8896   $275.89   $275.90   $275.90  
  Purchase #7 $182.37   4.322%   $190.252   $190.25   $190.25   $190.30  
  7 purchase totals = $1,246.45       $1,355.4663   $1,355.46   $1,355.50   $1,355.60