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 $68.49   4.386%   $71.494   $71.49   $71.50   $71.50  
  Purchase #2 $13.52   7.558%   $14.5418   $14.54   $14.55   $14.50  
  Purchase #3 $47.91   12.811%   $54.0478   $54.05   $54.05   $54.00  
  Purchase #4 $67.68   4.691%   $70.8549   $70.85   $70.85   $70.90  
  Purchase #5 $195.83   8.216%   $211.9194   $211.92   $211.90   $211.90  
  Purchase #6 $176.60   7.599%   $190.0198   $190.02   $190.00   $190.00  
  Purchase #7 $215.81   3.827%   $224.069   $224.07   $224.05   $224.10  
  7 purchase totals = $785.84       $836.9467   $836.94   $836.90   $836.90