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 $54.38   11.580%   $60.6772   $60.68   $60.70   $60.70  
  Purchase #2 $239.58   8.398%   $259.6999   $259.70   $259.70   $259.70  
  Purchase #3 $92.54   8.760%   $100.6465   $100.65   $100.65   $100.60  
  Purchase #4 $8.56   8.556%   $9.2924   $9.29   $9.30   $9.30  
  Purchase #5 $50.55   7.801%   $54.4934   $54.49   $54.50   $54.50  
  Purchase #6 $228.69   5.819%   $241.9975   $242.00   $242.00   $242.00  
  Purchase #7 $86.35   10.455%   $95.3779   $95.38   $95.40   $95.40  
  7 purchase totals = $760.65       $822.1848   $822.19   $822.25   $822.20