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 $36.69   8.675%   $39.8729   $39.87   $39.85   $39.90  
  Purchase #2 $222.41   11.225%   $247.3755   $247.38   $247.40   $247.40  
  Purchase #3 $149.62   12.412%   $168.1908   $168.19   $168.20   $168.20  
  Purchase #4 $145.43   4.670%   $152.2216   $152.22   $152.20   $152.20  
  Purchase #5 $139.67   4.611%   $146.1102   $146.11   $146.10   $146.10  
  Purchase #6 $101.51   12.216%   $113.9105   $113.91   $113.90   $113.90  
  Purchase #7 $7.29   13.451%   $8.2706   $8.27   $8.25   $8.30  
  7 purchase totals = $802.62       $875.9521   $875.95   $875.90   $876.00