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 $215.70   11.697%   $240.9304   $240.93   $240.95   $240.90  
  Purchase #2 $21.82   8.407%   $23.6544   $23.65   $23.65   $23.70  
  Purchase #3 $218.25   13.822%   $248.4165   $248.42   $248.40   $248.40  
  Purchase #4 $27.42   3.253%   $28.312   $28.31   $28.30   $28.30  
  Purchase #5 $85.85   10.706%   $95.0411   $95.04   $95.05   $95.00  
  Purchase #6 $222.49   3.689%   $230.6977   $230.70   $230.70   $230.70  
  Purchase #7 $207.32   11.211%   $230.5626   $230.56   $230.55   $230.60  
  7 purchase totals = $998.85       $1,097.6147   $1,097.61   $1,097.60   $1,097.60