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 $47.87   8.682%   $52.0261   $52.03   $52.05   $52.00  
  Purchase #2 $142.61   12.215%   $160.0298   $160.03   $160.05   $160.00  
  Purchase #3 $41.33   8.407%   $44.8046   $44.80   $44.80   $44.80  
  Purchase #4 $66.54   12.718%   $75.0026   $75.00   $75.00   $75.00  
  Purchase #5 $248.65   3.350%   $256.9798   $256.98   $257.00   $257.00  
  Purchase #6 $180.51   8.256%   $195.4129   $195.41   $195.40   $195.40  
  Purchase #7 $164.73   11.191%   $183.1649   $183.16   $183.15   $183.20  
  7 purchase totals = $892.24       $967.4207   $967.41   $967.45   $967.40