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 $24.47   8.161%   $26.467   $26.47   $26.45   $26.50  
  Purchase #2 $109.46   13.281%   $123.9974   $124.00   $124.00   $124.00  
  Purchase #3 $183.33   12.673%   $206.5634   $206.56   $206.55   $206.60  
  Purchase #4 $179.58   12.348%   $201.7545   $201.75   $201.75   $201.80  
  Purchase #5 $116.67   9.648%   $127.9263   $127.93   $127.95   $127.90  
  Purchase #6 $248.74   6.355%   $264.5474   $264.55   $264.55   $264.50  
  Purchase #7 $29.39   10.668%   $32.5253   $32.53   $32.55   $32.50  
  7 purchase totals = $891.64       $983.7813   $983.79   $983.80   $983.80