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 $88.99   6.326%   $94.6195   $94.62   $94.60   $94.60  
  Purchase #2 $34.96   10.537%   $38.6437   $38.64   $38.65   $38.60  
  Purchase #3 $75.77   5.220%   $79.7252   $79.73   $79.75   $79.70  
  Purchase #4 $236.44   5.665%   $249.8343   $249.83   $249.85   $249.80  
  Purchase #5 $20.61   3.445%   $21.32   $21.32   $21.30   $21.30  
  Purchase #6 $222.31   3.655%   $230.4354   $230.44   $230.45   $230.40  
  Purchase #7 $177.95   3.491%   $184.1622   $184.16   $184.15   $184.20  
  7 purchase totals = $857.03       $898.7403   $898.74   $898.75   $898.60