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 $94.85   13.556%   $107.7079   $107.71   $107.70   $107.70  
  Purchase #2 $10.88   4.732%   $11.3948   $11.39   $11.40   $11.40  
  Purchase #3 $197.93   8.394%   $214.5442   $214.54   $214.55   $214.50  
  Purchase #4 $32.95   6.380%   $35.0522   $35.05   $35.05   $35.10  
  Purchase #5 $169.95   13.353%   $192.6434   $192.64   $192.65   $192.60  
  Purchase #6 $94.99   12.712%   $107.0651   $107.07   $107.05   $107.10  
  Purchase #7 $126.72   10.736%   $140.3247   $140.32   $140.30   $140.30  
  7 purchase totals = $728.27       $808.7323   $808.72   $808.70   $808.70