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 $56.77   12.197%   $63.6942   $63.69   $63.70   $63.70  
  Purchase #2 $159.99   8.118%   $172.978   $172.98   $173.00   $173.00  
  Purchase #3 $42.37   11.781%   $47.3616   $47.36   $47.35   $47.40  
  Purchase #4 $210.63   7.217%   $225.8312   $225.83   $225.85   $225.80  
  Purchase #5 $43.76   5.777%   $46.288   $46.29   $46.30   $46.30  
  Purchase #6 $46.75   12.200%   $52.4535   $52.45   $52.45   $52.50  
  Purchase #7 $63.66   4.824%   $66.731   $66.73   $66.75   $66.70  
  7 purchase totals = $623.93       $675.3375   $675.33   $675.40   $675.40