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 $205.87   13.803%   $234.2862   $234.29   $234.30   $234.30  
  Purchase #2 $78.76   10.144%   $86.7494   $86.75   $86.75   $86.70  
  Purchase #3 $84.77   6.423%   $90.2148   $90.21   $90.20   $90.20  
  Purchase #4 $121.36   4.129%   $126.371   $126.37   $126.35   $126.40  
  Purchase #5 $175.65   12.622%   $197.8205   $197.82   $197.80   $197.80  
  Purchase #6 $24.44   11.870%   $27.341   $27.34   $27.35   $27.30  
  Purchase #7 $42.77   12.661%   $48.1851   $48.19   $48.20   $48.20  
  7 purchase totals = $733.62       $810.9680   $810.97   $810.95   $810.90