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 $248.49   8.422%   $269.4178   $269.42   $269.40   $269.40  
  Purchase #2 $137.60   4.106%   $143.2499   $143.25   $143.25   $143.20  
  Purchase #3 $123.75   3.872%   $128.5416   $128.54   $128.55   $128.50  
  Purchase #4 $73.79   11.862%   $82.543   $82.54   $82.55   $82.50  
  Purchase #5 $176.94   11.340%   $197.005   $197.01   $197.00   $197.00  
  Purchase #6 $19.49   6.210%   $20.7003   $20.70   $20.70   $20.70  
  Purchase #7 $216.67   6.564%   $230.8922   $230.89   $230.90   $230.90  
  7 purchase totals = $996.73       $1,072.3498   $1,072.35   $1,072.35   $1,072.20