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 $98.55   9.535%   $107.9467   $107.95   $107.95   $107.90  
  Purchase #2 $152.47   9.204%   $166.5033   $166.50   $166.50   $166.50  
  Purchase #3 $78.69   8.573%   $85.4361   $85.44   $85.45   $85.40  
  Purchase #4 $93.65   12.214%   $105.0884   $105.09   $105.10   $105.10  
  Purchase #5 $236.63   9.213%   $258.4307   $258.43   $258.45   $258.40  
  Purchase #6 $197.84   9.788%   $217.2046   $217.20   $217.20   $217.20  
  Purchase #7 $53.75   3.342%   $55.5463   $55.55   $55.55   $55.50  
  7 purchase totals = $911.58       $996.1561   $996.16   $996.20   $996.00