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 $33.80   4.598%   $35.3541   $35.35   $35.35   $35.40  
  Purchase #2 $239.94   7.494%   $257.9211   $257.92   $257.90   $257.90  
  Purchase #3 $63.41   8.282%   $68.6616   $68.66   $68.65   $68.70  
  Purchase #4 $136.98   11.747%   $153.071   $153.07   $153.05   $153.10  
  Purchase #5 $98.89   8.757%   $107.5498   $107.55   $107.55   $107.50  
  Purchase #6 $244.27   4.586%   $255.4722   $255.47   $255.45   $255.50  
  Purchase #7 $88.34   11.372%   $98.386   $98.39   $98.40   $98.40  
  7 purchase totals = $905.63       $976.4158   $976.41   $976.35   $976.50