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 $244.82   6.166%   $259.9156   $259.92   $259.90   $259.90  
  Purchase #2 $118.98   6.112%   $126.2521   $126.25   $126.25   $126.30  
  Purchase #3 $239.93   10.572%   $265.2954   $265.30   $265.30   $265.30  
  Purchase #4 $21.55   13.629%   $24.487   $24.49   $24.50   $24.50  
  Purchase #5 $231.25   11.767%   $258.4612   $258.46   $258.45   $258.50  
  Purchase #6 $150.32   5.463%   $158.532   $158.53   $158.55   $158.50  
  Purchase #7 $146.60   5.597%   $154.8052   $154.81   $154.80   $154.80  
  7 purchase totals = $1,153.45       $1,247.7485   $1,247.76   $1,247.75   $1,247.80