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 $52.49   8.411%   $56.9049   $56.90   $56.90   $56.90  
  Purchase #2 $151.40   8.337%   $164.0222   $164.02   $164.00   $164.00  
  Purchase #3 $129.49   8.398%   $140.3646   $140.36   $140.35   $140.40  
  Purchase #4 $114.92   9.322%   $125.6328   $125.63   $125.65   $125.60  
  Purchase #5 $54.66   3.698%   $56.6813   $56.68   $56.70   $56.70  
  Purchase #6 $170.26   12.656%   $191.8081   $191.81   $191.80   $191.80  
  Purchase #7 $117.96   5.345%   $124.265   $124.27   $124.25   $124.30  
  7 purchase totals = $791.18       $859.6789   $859.67   $859.65   $859.70