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 $58.46   8.162%   $63.2315   $63.23   $63.25   $63.20  
  Purchase #2 $164.30   9.346%   $179.6555   $179.66   $179.65   $179.70  
  Purchase #3 $176.88   9.313%   $193.3528   $193.35   $193.35   $193.40  
  Purchase #4 $76.31   8.494%   $82.7918   $82.79   $82.80   $82.80  
  Purchase #5 $197.49   8.558%   $214.3912   $214.39   $214.40   $214.40  
  Purchase #6 $133.51   4.113%   $139.0013   $139.00   $139.00   $139.00  
  Purchase #7 $188.28   13.853%   $214.3624   $214.36   $214.35   $214.40  
  7 purchase totals = $995.23       $1,086.7865   $1,086.78   $1,086.80   $1,086.90