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 $85.61   8.273%   $92.6925   $92.69   $92.70   $92.70  
  Purchase #2 $55.95   3.499%   $57.9077   $57.91   $57.90   $57.90  
  Purchase #3 $61.26   11.481%   $68.2933   $68.29   $68.30   $68.30  
  Purchase #4 $209.69   8.269%   $227.0293   $227.03   $227.05   $227.00  
  Purchase #5 $51.50   9.102%   $56.1875   $56.19   $56.20   $56.20  
  Purchase #6 $131.54   7.283%   $141.1201   $141.12   $141.10   $141.10  
  Purchase #7 $190.54   10.660%   $210.8516   $210.85   $210.85   $210.90  
  7 purchase totals = $786.09       $854.0820   $854.08   $854.10   $854.10