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 $69.44   4.838%   $72.7995   $72.80   $72.80   $72.80  
  Purchase #2 $203.75   12.742%   $229.7118   $229.71   $229.70   $229.70  
  Purchase #3 $34.88   6.317%   $37.0834   $37.08   $37.10   $37.10  
  Purchase #4 $212.93   13.261%   $241.1666   $241.17   $241.15   $241.20  
  Purchase #5 $30.80   12.388%   $34.6155   $34.62   $34.60   $34.60  
  Purchase #6 $193.31   7.865%   $208.5138   $208.51   $208.50   $208.50  
  Purchase #7 $130.90   3.692%   $135.7328   $135.73   $135.75   $135.70  
  7 purchase totals = $876.01       $959.6234   $959.62   $959.60   $959.60