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 $227.93   8.844%   $248.0881   $248.09   $248.10   $248.10  
  Purchase #2 $190.43   3.637%   $197.3559   $197.36   $197.35   $197.40  
  Purchase #3 $129.64   4.699%   $135.7318   $135.73   $135.75   $135.70  
  Purchase #4 $85.83   10.614%   $94.94   $94.94   $94.95   $94.90  
  Purchase #5 $51.72   9.728%   $56.7513   $56.75   $56.75   $56.80  
  Purchase #6 $151.29   5.520%   $159.6412   $159.64   $159.65   $159.60  
  Purchase #7 $135.38   13.785%   $154.0421   $154.04   $154.05   $154.00  
  7 purchase totals = $972.22       $1,046.5504   $1,046.55   $1,046.60   $1,046.50