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 $56.59   5.662%   $59.7941   $59.79   $59.80   $59.80  
  Purchase #2 $237.72   12.590%   $267.6489   $267.65   $267.65   $267.60  
  Purchase #3 $248.76   4.387%   $259.6731   $259.67   $259.65   $259.70  
  Purchase #4 $148.71   4.595%   $155.5432   $155.54   $155.55   $155.50  
  Purchase #5 $175.36   7.862%   $189.1468   $189.15   $189.15   $189.10  
  Purchase #6 $122.76   9.204%   $134.0588   $134.06   $134.05   $134.10  
  Purchase #7 $34.58   4.842%   $36.2544   $36.25   $36.25   $36.30  
  7 purchase totals = $1,024.48       $1,102.1193   $1,102.11   $1,102.10   $1,102.10