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 $121.64   3.582%   $125.9971   $126.00   $126.00   $126.00  
  Purchase #2 $248.95   13.386%   $282.2744   $282.27   $282.25   $282.30  
  Purchase #3 $236.35   9.657%   $259.1743   $259.17   $259.15   $259.20  
  Purchase #4 $24.25   6.163%   $25.7445   $25.74   $25.75   $25.70  
  Purchase #5 $95.77   13.446%   $108.6472   $108.65   $108.65   $108.60  
  Purchase #6 $237.61   10.210%   $261.87   $261.87   $261.85   $261.90  
  Purchase #7 $67.74   3.384%   $70.0323   $70.03   $70.05   $70.00  
  7 purchase totals = $1,032.31       $1,133.7398   $1,133.73   $1,133.70   $1,133.70