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 $14.31   13.573%   $16.2523   $16.25   $16.25   $16.30  
  Purchase #2 $64.47   10.157%   $71.0182   $71.02   $71.00   $71.00  
  Purchase #3 $78.56   3.734%   $81.4934   $81.49   $81.50   $81.50  
  Purchase #4 $76.96   12.748%   $86.7709   $86.77   $86.75   $86.80  
  Purchase #5 $202.74   8.813%   $220.6075   $220.61   $220.60   $220.60  
  Purchase #6 $198.39   12.211%   $222.6154   $222.62   $222.60   $222.60  
  Purchase #7 $53.53   5.555%   $56.5036   $56.50   $56.50   $56.50  
  7 purchase totals = $688.96       $755.2613   $755.26   $755.20   $755.30