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 $248.69   13.679%   $282.7083   $282.71   $282.70   $282.70  
  Purchase #2 $234.94   10.425%   $259.4325   $259.43   $259.45   $259.40  
  Purchase #3 $139.53   7.219%   $149.6027   $149.60   $149.60   $149.60  
  Purchase #4 $5.28   11.749%   $5.9003   $5.90   $5.90   $5.90  
  Purchase #5 $131.31   9.633%   $143.9591   $143.96   $143.95   $144.00  
  Purchase #6 $61.30   4.241%   $63.8997   $63.90   $63.90   $63.90  
  Purchase #7 $162.57   5.447%   $171.4252   $171.43   $171.45   $171.40  
  7 purchase totals = $983.62       $1,076.9278   $1,076.93   $1,076.95   $1,076.90