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 $236.34   11.691%   $263.9705   $263.97   $263.95   $264.00  
  Purchase #2 $210.35   3.264%   $217.2158   $217.22   $217.20   $217.20  
  Purchase #3 $249.25   6.508%   $265.4712   $265.47   $265.45   $265.50  
  Purchase #4 $246.69   3.304%   $254.8406   $254.84   $254.85   $254.80  
  Purchase #5 $187.61   10.647%   $207.5848   $207.58   $207.60   $207.60  
  Purchase #6 $199.55   3.177%   $205.8897   $205.89   $205.90   $205.90  
  Purchase #7 $198.93   10.850%   $220.5139   $220.51   $220.50   $220.50  
  7 purchase totals = $1,528.72       $1,635.4865   $1,635.48   $1,635.45   $1,635.50