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 $50.99   5.103%   $53.592   $53.59   $53.60   $53.60  
  Purchase #2 $90.69   8.779%   $98.6517   $98.65   $98.65   $98.70  
  Purchase #3 $74.74   12.467%   $84.0578   $84.06   $84.05   $84.10  
  Purchase #4 $199.49   11.676%   $222.7825   $222.78   $222.80   $222.80  
  Purchase #5 $119.30   4.335%   $124.4717   $124.47   $124.45   $124.50  
  Purchase #6 $239.92   7.201%   $257.1966   $257.20   $257.20   $257.20  
  Purchase #7 $234.88   4.577%   $245.6305   $245.63   $245.65   $245.60  
  7 purchase totals = $1,010.01       $1,086.3828   $1,086.38   $1,086.40   $1,086.50