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 $224.71   11.682%   $250.9606   $250.96   $250.95   $251.00  
  Purchase #2 $46.92   10.320%   $51.7621   $51.76   $51.75   $51.80  
  Purchase #3 $101.87   11.336%   $113.418   $113.42   $113.40   $113.40  
  Purchase #4 $199.26   5.667%   $210.5521   $210.55   $210.55   $210.60  
  Purchase #5 $193.80   3.638%   $200.8504   $200.85   $200.85   $200.90  
  Purchase #6 $220.87   6.276%   $234.7318   $234.73   $234.75   $234.70  
  Purchase #7 $86.89   7.382%   $93.3042   $93.30   $93.30   $93.30  
  7 purchase totals = $1,074.32       $1,155.5792   $1,155.57   $1,155.55   $1,155.70