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 $110.72   13.776%   $125.9728   $125.97   $125.95   $126.00  
  Purchase #2 $157.80   12.169%   $177.0027   $177.00   $177.00   $177.00  
  Purchase #3 $93.41   13.749%   $106.2529   $106.25   $106.25   $106.30  
  Purchase #4 $49.64   10.412%   $54.8085   $54.81   $54.80   $54.80  
  Purchase #5 $206.76   13.516%   $234.7057   $234.71   $234.70   $234.70  
  Purchase #6 $73.65   9.127%   $80.372   $80.37   $80.35   $80.40  
  Purchase #7 $64.75   12.813%   $73.0464   $73.05   $73.05   $73.00  
  7 purchase totals = $756.73       $852.1610   $852.16   $852.10   $852.20