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 $152.61   10.637%   $168.8431   $168.84   $168.85   $168.80  
  Purchase #2 $78.76   7.421%   $84.6048   $84.60   $84.60   $84.60  
  Purchase #3 $102.47   10.714%   $113.4486   $113.45   $113.45   $113.40  
  Purchase #4 $107.49   6.355%   $114.321   $114.32   $114.30   $114.30  
  Purchase #5 $247.98   12.324%   $278.5411   $278.54   $278.55   $278.50  
  Purchase #6 $101.65   12.824%   $114.6856   $114.69   $114.70   $114.70  
  Purchase #7 $123.99   10.340%   $136.8106   $136.81   $136.80   $136.80  
  7 purchase totals = $914.95       $1,011.2548   $1,011.25   $1,011.25   $1,011.10