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 $69.97   8.287%   $75.7684   $75.77   $75.75   $75.80  
  Purchase #2 $46.87   13.445%   $53.1717   $53.17   $53.15   $53.20  
  Purchase #3 $108.29   5.331%   $114.0629   $114.06   $114.05   $114.10  
  Purchase #4 $119.76   13.732%   $136.2054   $136.21   $136.20   $136.20  
  Purchase #5 $142.49   6.475%   $151.7162   $151.72   $151.70   $151.70  
  Purchase #6 $9.35   12.772%   $10.5442   $10.54   $10.55   $10.50  
  Purchase #7 $225.50   13.409%   $255.7373   $255.74   $255.75   $255.70  
  7 purchase totals = $722.23       $797.2061   $797.21   $797.15   $797.20