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 $225.95   6.857%   $241.4434   $241.44   $241.45   $241.40  
  Purchase #2 $69.99   5.273%   $73.6806   $73.68   $73.70   $73.70  
  Purchase #3 $11.95   9.200%   $13.0494   $13.05   $13.05   $13.00  
  Purchase #4 $125.68   8.431%   $136.2761   $136.28   $136.30   $136.30  
  Purchase #5 $161.67   8.775%   $175.8565   $175.86   $175.85   $175.90  
  Purchase #6 $202.34   12.669%   $227.9745   $227.97   $227.95   $228.00  
  Purchase #7 $22.75   9.334%   $24.8735   $24.87   $24.85   $24.90  
  7 purchase totals = $820.33       $893.1540   $893.15   $893.15   $893.20