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 $55.93   12.451%   $62.8938   $62.89   $62.90   $62.90  
  Purchase #2 $129.79   10.432%   $143.3297   $143.33   $143.35   $143.30  
  Purchase #3 $144.35   5.508%   $152.3008   $152.30   $152.30   $152.30  
  Purchase #4 $203.92   6.227%   $216.6181   $216.62   $216.60   $216.60  
  Purchase #5 $46.37   6.368%   $49.3228   $49.32   $49.30   $49.30  
  Purchase #6 $100.83   13.288%   $114.2283   $114.23   $114.25   $114.20  
  Purchase #7 $14.36   7.618%   $15.4539   $15.45   $15.45   $15.50  
  7 purchase totals = $695.55       $754.1474   $754.14   $754.15   $754.10