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 $14.81   11.866%   $16.5674   $16.57   $16.55   $16.60  
  Purchase #2 $118.56   3.484%   $122.6906   $122.69   $122.70   $122.70  
  Purchase #3 $44.59   5.851%   $47.199   $47.20   $47.20   $47.20  
  Purchase #4 $174.65   13.527%   $198.2749   $198.27   $198.25   $198.30  
  Purchase #5 $54.82   6.377%   $58.3159   $58.32   $58.30   $58.30  
  Purchase #6 $208.37   7.217%   $223.4081   $223.41   $223.40   $223.40  
  Purchase #7 $141.36   9.834%   $155.2613   $155.26   $155.25   $155.30  
  7 purchase totals = $757.16       $821.7172   $821.72   $821.65   $821.80