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 $56.67   6.218%   $60.1937   $60.19   $60.20   $60.20  
  Purchase #2 $135.40   3.549%   $140.2053   $140.21   $140.20   $140.20  
  Purchase #3 $95.77   9.625%   $104.9879   $104.99   $105.00   $105.00  
  Purchase #4 $88.60   12.656%   $99.8132   $99.81   $99.80   $99.80  
  Purchase #5 $127.54   10.186%   $140.5312   $140.53   $140.55   $140.50  
  Purchase #6 $248.51   6.312%   $264.196   $264.20   $264.20   $264.20  
  Purchase #7 $246.27   6.341%   $261.886   $261.89   $261.90   $261.90  
  7 purchase totals = $998.76       $1,071.8133   $1,071.82   $1,071.85   $1,071.80