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 $44.66   6.839%   $47.7143   $47.71   $47.70   $47.70  
  Purchase #2 $248.39   9.873%   $272.9135   $272.91   $272.90   $272.90  
  Purchase #3 $134.97   7.684%   $145.3411   $145.34   $145.35   $145.30  
  Purchase #4 $155.94   5.209%   $164.0629   $164.06   $164.05   $164.10  
  Purchase #5 $83.26   11.359%   $92.7175   $92.72   $92.70   $92.70  
  Purchase #6 $19.96   11.837%   $22.3227   $22.32   $22.30   $22.30  
  Purchase #7 $227.35   5.434%   $239.7042   $239.70   $239.70   $239.70  
  7 purchase totals = $914.53       $984.7762   $984.76   $984.70   $984.70