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 $245.51   12.497%   $276.1914   $276.19   $276.20   $276.20  
  Purchase #2 $21.77   9.742%   $23.8908   $23.89   $23.90   $23.90  
  Purchase #3 $26.61   8.172%   $28.7846   $28.78   $28.80   $28.80  
  Purchase #4 $208.46   5.447%   $219.8148   $219.81   $219.80   $219.80  
  Purchase #5 $118.61   13.742%   $134.9094   $134.91   $134.90   $134.90  
  Purchase #6 $129.27   3.177%   $133.3769   $133.38   $133.40   $133.40  
  Purchase #7 $172.69   10.844%   $191.4165   $191.42   $191.40   $191.40  
  7 purchase totals = $922.92       $1,008.3844   $1,008.38   $1,008.40   $1,008.40