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 $205.33   5.571%   $216.7689   $216.77   $216.75   $216.80  
  Purchase #2 $81.55   4.162%   $84.9441   $84.94   $84.95   $84.90  
  Purchase #3 $38.51   13.136%   $43.5687   $43.57   $43.55   $43.60  
  Purchase #4 $59.67   6.290%   $63.4232   $63.42   $63.40   $63.40  
  Purchase #5 $230.84   3.764%   $239.5288   $239.53   $239.55   $239.50  
  Purchase #6 $207.88   3.175%   $214.4802   $214.48   $214.50   $214.50  
  Purchase #7 $175.89   3.474%   $182.0004   $182.00   $182.00   $182.00  
  7 purchase totals = $999.67       $1,044.7143   $1,044.71   $1,044.70   $1,044.70