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 $43.84   7.270%   $47.0272   $47.03   $47.05   $47.00  
  Purchase #2 $208.54   9.231%   $227.7903   $227.79   $227.80   $227.80  
  Purchase #3 $242.48   12.462%   $272.6979   $272.70   $272.70   $272.70  
  Purchase #4 $183.36   13.206%   $207.5745   $207.57   $207.55   $207.60  
  Purchase #5 $8.27   6.848%   $8.8363   $8.84   $8.85   $8.80  
  Purchase #6 $11.77   7.554%   $12.6591   $12.66   $12.65   $12.70  
  Purchase #7 $114.95   5.416%   $121.1757   $121.18   $121.20   $121.20  
  7 purchase totals = $813.21       $897.7610   $897.77   $897.80   $897.80