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 $44.43   5.267%   $46.7701   $46.77   $46.75   $46.80  
  Purchase #2 $108.42   7.564%   $116.6209   $116.62   $116.60   $116.60  
  Purchase #3 $146.68   13.595%   $166.6211   $166.62   $166.60   $166.60  
  Purchase #4 $7.70   12.834%   $8.6882   $8.69   $8.70   $8.70  
  Purchase #5 $62.51   7.444%   $67.1632   $67.16   $67.15   $67.20  
  Purchase #6 $65.58   10.709%   $72.603   $72.60   $72.60   $72.60  
  Purchase #7 $222.90   7.582%   $239.8003   $239.80   $239.80   $239.80  
  7 purchase totals = $658.22       $718.2668   $718.26   $718.20   $718.30