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 $47.33   13.268%   $53.6097   $53.61   $53.60   $53.60  
  Purchase #2 $218.88   11.641%   $244.3598   $244.36   $244.35   $244.40  
  Purchase #3 $74.55   13.329%   $84.4868   $84.49   $84.50   $84.50  
  Purchase #4 $17.38   5.799%   $18.3879   $18.39   $18.40   $18.40  
  Purchase #5 $82.61   4.822%   $86.5935   $86.59   $86.60   $86.60  
  Purchase #6 $211.51   4.870%   $221.8105   $221.81   $221.80   $221.80  
  Purchase #7 $38.46   6.569%   $40.9864   $40.99   $41.00   $41.00  
  7 purchase totals = $690.72       $750.2346   $750.24   $750.25   $750.30