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 $200.54   3.241%   $207.0395   $207.04   $207.05   $207.00  
  Purchase #2 $153.28   8.316%   $166.0268   $166.03   $166.05   $166.00  
  Purchase #3 $162.34   6.255%   $172.4944   $172.49   $172.50   $172.50  
  Purchase #4 $243.99   4.317%   $254.523   $254.52   $254.50   $254.50  
  Purchase #5 $90.80   12.864%   $102.4805   $102.48   $102.50   $102.50  
  Purchase #6 $201.66   12.720%   $227.3112   $227.31   $227.30   $227.30  
  Purchase #7 $214.71   6.453%   $228.5652   $228.57   $228.55   $228.60  
  7 purchase totals = $1,267.32       $1,358.4406   $1,358.44   $1,358.45   $1,358.40