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 $199.66   13.583%   $226.7798   $226.78   $226.80   $226.80  
  Purchase #2 $191.55   7.141%   $205.2286   $205.23   $205.25   $205.20  
  Purchase #3 $116.95   8.404%   $126.7785   $126.78   $126.80   $126.80  
  Purchase #4 $57.44   6.811%   $61.3522   $61.35   $61.35   $61.40  
  Purchase #5 $183.64   12.596%   $206.7713   $206.77   $206.75   $206.80  
  Purchase #6 $54.59   7.850%   $58.8753   $58.88   $58.90   $58.90  
  Purchase #7 $150.76   12.856%   $170.1417   $170.14   $170.15   $170.10  
  7 purchase totals = $954.59       $1,055.9274   $1,055.93   $1,056.00   $1,056.00