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 $231.29   11.858%   $258.7164   $258.72   $258.70   $258.70  
  Purchase #2 $155.43   11.622%   $173.4941   $173.49   $173.50   $173.50  
  Purchase #3 $98.25   11.288%   $109.3405   $109.34   $109.35   $109.30  
  Purchase #4 $152.97   5.874%   $161.9555   $161.96   $161.95   $162.00  
  Purchase #5 $54.25   10.543%   $59.9696   $59.97   $59.95   $60.00  
  Purchase #6 $51.37   11.383%   $57.2174   $57.22   $57.20   $57.20  
  Purchase #7 $220.96   8.151%   $238.9704   $238.97   $238.95   $239.00  
  7 purchase totals = $964.52       $1,059.6639   $1,059.67   $1,059.60   $1,059.70