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 $50.28   11.849%   $56.2377   $56.24   $56.25   $56.20  
  Purchase #2 $70.28   5.248%   $73.9683   $73.97   $73.95   $74.00  
  Purchase #3 $174.37   11.217%   $193.9291   $193.93   $193.95   $193.90  
  Purchase #4 $247.33   7.380%   $265.583   $265.58   $265.60   $265.60  
  Purchase #5 $86.89   5.738%   $91.8757   $91.88   $91.90   $91.90  
  Purchase #6 $114.91   11.732%   $128.3912   $128.39   $128.40   $128.40  
  Purchase #7 $14.85   7.697%   $15.993   $15.99   $16.00   $16.00  
  7 purchase totals = $758.91       $825.9780   $825.98   $826.05   $826.00