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 $146.59   8.208%   $158.6221   $158.62   $158.60   $158.60  
  Purchase #2 $229.49   4.847%   $240.6134   $240.61   $240.60   $240.60  
  Purchase #3 $229.33   4.515%   $239.6842   $239.68   $239.70   $239.70  
  Purchase #4 $174.53   5.302%   $183.7836   $183.78   $183.80   $183.80  
  Purchase #5 $219.59   4.675%   $229.8558   $229.86   $229.85   $229.90  
  Purchase #6 $168.36   3.471%   $174.2038   $174.20   $174.20   $174.20  
  Purchase #7 $46.25   6.242%   $49.1369   $49.14   $49.15   $49.10  
  7 purchase totals = $1,214.14       $1,275.8998   $1,275.89   $1,275.90   $1,275.90