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 $121.54   3.294%   $125.5435   $125.54   $125.55   $125.50  
  Purchase #2 $63.56   4.725%   $66.5632   $66.56   $66.55   $66.60  
  Purchase #3 $194.65   6.127%   $206.5762   $206.58   $206.60   $206.60  
  Purchase #4 $162.26   5.195%   $170.6894   $170.69   $170.70   $170.70  
  Purchase #5 $207.64   3.335%   $214.5648   $214.56   $214.55   $214.60  
  Purchase #6 $148.59   7.322%   $159.4698   $159.47   $159.45   $159.50  
  Purchase #7 $189.39   4.665%   $198.225   $198.23   $198.25   $198.20  
  7 purchase totals = $1,087.63       $1,141.6319   $1,141.63   $1,141.65   $1,141.70