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 $232.61   13.603%   $264.2519   $264.25   $264.25   $264.30  
  Purchase #2 $11.85   10.457%   $13.0892   $13.09   $13.10   $13.10  
  Purchase #3 $238.73   5.863%   $252.7267   $252.73   $252.75   $252.70  
  Purchase #4 $232.40   4.867%   $243.7109   $243.71   $243.70   $243.70  
  Purchase #5 $116.49   8.246%   $126.0958   $126.10   $126.10   $126.10  
  Purchase #6 $36.40   3.803%   $37.7843   $37.78   $37.80   $37.80  
  Purchase #7 $186.85   5.331%   $196.811   $196.81   $196.80   $196.80  
  7 purchase totals = $1,055.33       $1,134.4698   $1,134.47   $1,134.50   $1,134.50