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 $58.85   11.737%   $65.7572   $65.76   $65.75   $65.80  
  Purchase #2 $42.71   11.816%   $47.7566   $47.76   $47.75   $47.80  
  Purchase #3 $26.76   9.320%   $29.254   $29.25   $29.25   $29.30  
  Purchase #4 $203.91   8.419%   $221.0772   $221.08   $221.10   $221.10  
  Purchase #5 $102.43   3.334%   $105.845   $105.85   $105.85   $105.80  
  Purchase #6 $176.99   3.821%   $183.7528   $183.75   $183.75   $183.80  
  Purchase #7 $114.89   13.275%   $130.1416   $130.14   $130.15   $130.10  
  7 purchase totals = $726.54       $783.5844   $783.59   $783.60   $783.70