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 $87.36   5.687%   $92.3282   $92.33   $92.35   $92.30  
  Purchase #2 $59.33   6.303%   $63.0696   $63.07   $63.05   $63.10  
  Purchase #3 $234.88   4.567%   $245.607   $245.61   $245.60   $245.60  
  Purchase #4 $81.69   12.374%   $91.7983   $91.80   $91.80   $91.80  
  Purchase #5 $32.29   9.302%   $35.2936   $35.29   $35.30   $35.30  
  Purchase #6 $240.82   4.823%   $252.4347   $252.43   $252.45   $252.40  
  Purchase #7 $166.95   5.866%   $176.7433   $176.74   $176.75   $176.70  
  7 purchase totals = $903.32       $957.2747   $957.27   $957.30   $957.20