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 $249.44   6.842%   $266.5067   $266.51   $266.50   $266.50  
  Purchase #2 $184.68   8.183%   $199.7924   $199.79   $199.80   $199.80  
  Purchase #3 $113.25   7.625%   $121.8853   $121.89   $121.90   $121.90  
  Purchase #4 $5.56   5.738%   $5.879   $5.88   $5.90   $5.90  
  Purchase #5 $180.60   9.247%   $197.3001   $197.30   $197.30   $197.30  
  Purchase #6 $182.72   13.143%   $206.7349   $206.73   $206.75   $206.70  
  Purchase #7 $95.46   12.547%   $107.4374   $107.44   $107.45   $107.40  
  7 purchase totals = $1,011.71       $1,105.5358   $1,105.54   $1,105.60   $1,105.50