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 $206.57   11.845%   $231.0382   $231.04   $231.05   $231.00  
  Purchase #2 $200.56   9.506%   $219.6252   $219.63   $219.65   $219.60  
  Purchase #3 $193.86   8.868%   $211.0515   $211.05   $211.05   $211.10  
  Purchase #4 $35.81   6.750%   $38.2272   $38.23   $38.25   $38.20  
  Purchase #5 $47.95   8.692%   $52.1178   $52.12   $52.10   $52.10  
  Purchase #6 $117.42   3.865%   $121.9583   $121.96   $121.95   $122.00  
  Purchase #7 $72.65   5.193%   $76.4227   $76.42   $76.40   $76.40  
  7 purchase totals = $874.82       $950.4409   $950.45   $950.45   $950.40