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 $51.94   13.553%   $58.9794   $58.98   $59.00   $59.00  
  Purchase #2 $105.79   6.848%   $113.0345   $113.03   $113.05   $113.00  
  Purchase #3 $181.92   10.803%   $201.5728   $201.57   $201.55   $201.60  
  Purchase #4 $122.67   8.477%   $133.0687   $133.07   $133.05   $133.10  
  Purchase #5 $212.77   12.552%   $239.4769   $239.48   $239.50   $239.50  
  Purchase #6 $211.65   8.748%   $230.1651   $230.17   $230.15   $230.20  
  Purchase #7 $250.94   5.402%   $264.4958   $264.50   $264.50   $264.50  
  7 purchase totals = $1,137.68       $1,240.7932   $1,240.80   $1,240.80   $1,240.90