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 $233.41   13.654%   $265.2798   $265.28   $265.30   $265.30  
  Purchase #2 $220.32   6.609%   $234.8809   $234.88   $234.90   $234.90  
  Purchase #3 $79.56   5.673%   $84.0734   $84.07   $84.05   $84.10  
  Purchase #4 $60.42   4.601%   $63.1999   $63.20   $63.20   $63.20  
  Purchase #5 $98.79   6.313%   $105.0266   $105.03   $105.05   $105.00  
  Purchase #6 $41.51   5.666%   $43.862   $43.86   $43.85   $43.90  
  Purchase #7 $190.28   6.867%   $203.3465   $203.35   $203.35   $203.30  
  7 purchase totals = $924.29       $999.6691   $999.67   $999.70   $999.70