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 $237.69   12.714%   $267.9099   $267.91   $267.90   $267.90  
  Purchase #2 $175.80   6.261%   $186.8068   $186.81   $186.80   $186.80  
  Purchase #3 $209.57   8.167%   $226.6856   $226.69   $226.70   $226.70  
  Purchase #4 $6.35   6.273%   $6.7483   $6.75   $6.75   $6.70  
  Purchase #5 $242.31   5.385%   $255.3584   $255.36   $255.35   $255.40  
  Purchase #6 $134.75   8.540%   $146.2577   $146.26   $146.25   $146.30  
  Purchase #7 $156.49   3.802%   $162.4397   $162.44   $162.45   $162.40  
  7 purchase totals = $1,162.96       $1,252.2064   $1,252.22   $1,252.20   $1,252.20