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 $80.56   5.134%   $84.696   $84.70   $84.70   $84.70  
  Purchase #2 $103.70   12.648%   $116.816   $116.82   $116.80   $116.80  
  Purchase #3 $70.58   8.679%   $76.7056   $76.71   $76.70   $76.70  
  Purchase #4 $157.69   11.582%   $175.9537   $175.95   $175.95   $176.00  
  Purchase #5 $92.56   12.372%   $104.0115   $104.01   $104.00   $104.00  
  Purchase #6 $154.42   9.525%   $169.1285   $169.13   $169.15   $169.10  
  Purchase #7 $195.95   13.649%   $222.6952   $222.70   $222.70   $222.70  
  7 purchase totals = $855.46       $950.0065   $950.02   $950.00   $950.00