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 $25.69   3.654%   $26.6287   $26.63   $26.65   $26.60  
  Purchase #2 $174.66   13.601%   $198.4155   $198.42   $198.40   $198.40  
  Purchase #3 $227.35   13.386%   $257.7831   $257.78   $257.80   $257.80  
  Purchase #4 $118.40   12.109%   $132.7371   $132.74   $132.75   $132.70  
  Purchase #5 $125.48   3.124%   $129.4   $129.40   $129.40   $129.40  
  Purchase #6 $211.83   5.135%   $222.7075   $222.71   $222.70   $222.70  
  Purchase #7 $89.73   8.857%   $97.6774   $97.68   $97.70   $97.70  
  7 purchase totals = $973.14       $1,065.3493   $1,065.36   $1,065.40   $1,065.30