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 $246.94   11.646%   $275.6986   $275.70   $275.70   $275.70  
  Purchase #2 $204.94   9.461%   $224.3294   $224.33   $224.35   $224.30  
  Purchase #3 $115.74   7.513%   $124.4355   $124.44   $124.45   $124.40  
  Purchase #4 $24.34   5.335%   $25.6385   $25.64   $25.65   $25.60  
  Purchase #5 $42.88   10.194%   $47.2512   $47.25   $47.25   $47.30  
  Purchase #6 $134.92   8.402%   $146.256   $146.26   $146.25   $146.30  
  Purchase #7 $146.71   7.464%   $157.6604   $157.66   $157.65   $157.70  
  7 purchase totals = $916.47       $1,001.2696   $1,001.28   $1,001.30   $1,001.30