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 $60.72   12.871%   $68.5353   $68.54   $68.55   $68.50  
  Purchase #2 $228.91   8.391%   $248.1178   $248.12   $248.10   $248.10  
  Purchase #3 $78.81   8.137%   $85.2228   $85.22   $85.20   $85.20  
  Purchase #4 $81.58   12.629%   $91.8827   $91.88   $91.90   $91.90  
  Purchase #5 $72.38   13.167%   $81.9103   $81.91   $81.90   $81.90  
  Purchase #6 $15.29   9.223%   $16.7002   $16.70   $16.70   $16.70  
  Purchase #7 $39.66   7.709%   $42.7174   $42.72   $42.70   $42.70  
  7 purchase totals = $577.35       $635.0865   $635.09   $635.05   $635.00