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 $152.66   6.617%   $162.7615   $162.76   $162.75   $162.80  
  Purchase #2 $216.58   9.160%   $236.4187   $236.42   $236.40   $236.40  
  Purchase #3 $117.32   9.633%   $128.6214   $128.62   $128.60   $128.60  
  Purchase #4 $199.80   3.517%   $206.827   $206.83   $206.85   $206.80  
  Purchase #5 $74.49   3.575%   $77.153   $77.15   $77.15   $77.20  
  Purchase #6 $241.69   8.373%   $261.9267   $261.93   $261.95   $261.90  
  Purchase #7 $222.81   11.179%   $247.7179   $247.72   $247.70   $247.70  
  7 purchase totals = $1,225.35       $1,321.4262   $1,321.43   $1,321.40   $1,321.40