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 $238.40   9.495%   $261.0361   $261.04   $261.05   $261.00  
  Purchase #2 $113.29   6.593%   $120.7592   $120.76   $120.75   $120.80  
  Purchase #3 $43.63   9.698%   $47.8612   $47.86   $47.85   $47.90  
  Purchase #4 $156.58   6.378%   $166.5667   $166.57   $166.55   $166.60  
  Purchase #5 $162.55   10.247%   $179.2065   $179.21   $179.20   $179.20  
  Purchase #6 $17.89   11.160%   $19.8865   $19.89   $19.90   $19.90  
  Purchase #7 $250.49   3.202%   $258.5107   $258.51   $258.50   $258.50  
  7 purchase totals = $982.83       $1,053.8269   $1,053.84   $1,053.80   $1,053.90