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 $219.86   13.543%   $249.6356   $249.64   $249.65   $249.60  
  Purchase #2 $199.27   10.443%   $220.0798   $220.08   $220.10   $220.10  
  Purchase #3 $116.73   9.586%   $127.9197   $127.92   $127.90   $127.90  
  Purchase #4 $177.87   10.605%   $196.7331   $196.73   $196.75   $196.70  
  Purchase #5 $205.66   5.297%   $216.5538   $216.55   $216.55   $216.60  
  Purchase #6 $127.80   4.805%   $133.9408   $133.94   $133.95   $133.90  
  Purchase #7 $227.90   9.656%   $249.906   $249.91   $249.90   $249.90  
  7 purchase totals = $1,275.09       $1,394.7688   $1,394.77   $1,394.80   $1,394.70