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 $54.89   12.673%   $61.8462   $61.85   $61.85   $61.80  
  Purchase #2 $146.41   10.548%   $161.8533   $161.85   $161.85   $161.90  
  Purchase #3 $76.46   4.208%   $79.6774   $79.68   $79.70   $79.70  
  Purchase #4 $197.55   7.573%   $212.5105   $212.51   $212.50   $212.50  
  Purchase #5 $19.97   6.630%   $21.294   $21.29   $21.30   $21.30  
  Purchase #6 $96.31   9.696%   $105.6482   $105.65   $105.65   $105.60  
  Purchase #7 $158.87   5.670%   $167.8779   $167.88   $167.90   $167.90  
  7 purchase totals = $750.46       $810.7075   $810.71   $810.75   $810.70