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 $106.66   11.712%   $119.152   $119.15   $119.15   $119.20  
  Purchase #2 $115.61   6.522%   $123.1501   $123.15   $123.15   $123.20  
  Purchase #3 $35.62   8.675%   $38.71   $38.71   $38.70   $38.70  
  Purchase #4 $49.27   6.637%   $52.54   $52.54   $52.55   $52.50  
  Purchase #5 $237.79   8.525%   $258.0616   $258.06   $258.05   $258.10  
  Purchase #6 $186.33   9.115%   $203.314   $203.31   $203.30   $203.30  
  Purchase #7 $67.74   9.422%   $74.1225   $74.12   $74.10   $74.10  
  7 purchase totals = $799.02       $869.0502   $869.04   $869.00   $869.10