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 $23.83   9.633%   $26.1255   $26.13   $26.15   $26.10  
  Purchase #2 $240.33   8.164%   $259.9505   $259.95   $259.95   $260.00  
  Purchase #3 $192.96   3.507%   $199.7271   $199.73   $199.75   $199.70  
  Purchase #4 $237.52   5.546%   $250.6929   $250.69   $250.70   $250.70  
  Purchase #5 $126.89   7.603%   $136.5374   $136.54   $136.55   $136.50  
  Purchase #6 $106.28   3.176%   $109.6555   $109.66   $109.65   $109.70  
  Purchase #7 $250.86   11.112%   $278.7356   $278.74   $278.75   $278.70  
  7 purchase totals = $1,178.67       $1,261.4245   $1,261.44   $1,261.50   $1,261.40