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 $35.63   13.175%   $40.3243   $40.32   $40.30   $40.30  
  Purchase #2 $163.31   9.686%   $179.1282   $179.13   $179.15   $179.10  
  Purchase #3 $215.55   7.633%   $232.0029   $232.00   $232.00   $232.00  
  Purchase #4 $175.63   6.472%   $186.9968   $187.00   $187.00   $187.00  
  Purchase #5 $160.33   3.744%   $166.3328   $166.33   $166.35   $166.30  
  Purchase #6 $170.99   6.146%   $181.499   $181.50   $181.50   $181.50  
  Purchase #7 $38.63   3.791%   $40.0945   $40.09   $40.10   $40.10  
  7 purchase totals = $960.07       $1,026.3785   $1,026.37   $1,026.40   $1,026.30