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 $129.83   12.464%   $146.012   $146.01   $146.00   $146.00  
  Purchase #2 $89.32   7.224%   $95.7725   $95.77   $95.75   $95.80  
  Purchase #3 $21.61   11.693%   $24.1369   $24.14   $24.15   $24.10  
  Purchase #4 $54.66   12.842%   $61.6794   $61.68   $61.70   $61.70  
  Purchase #5 $113.46   4.800%   $118.9061   $118.91   $118.90   $118.90  
  Purchase #6 $11.75   7.678%   $12.6522   $12.65   $12.65   $12.70  
  Purchase #7 $74.44   3.185%   $76.8109   $76.81   $76.80   $76.80  
  7 purchase totals = $495.07       $535.9700   $535.97   $535.95   $536.00