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 $229.35   8.547%   $248.9525   $248.95   $248.95   $249.00  
  Purchase #2 $55.68   5.799%   $58.9089   $58.91   $58.90   $58.90  
  Purchase #3 $201.89   11.775%   $225.6625   $225.66   $225.65   $225.70  
  Purchase #4 $179.32   10.214%   $197.6357   $197.64   $197.65   $197.60  
  Purchase #5 $5.64   7.118%   $6.0415   $6.04   $6.05   $6.00  
  Purchase #6 $189.65   3.634%   $196.5419   $196.54   $196.55   $196.50  
  Purchase #7 $145.93   5.398%   $153.8073   $153.81   $153.80   $153.80  
  7 purchase totals = $1,007.46       $1,087.5503   $1,087.55   $1,087.55   $1,087.50