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 $175.38   11.823%   $196.1152   $196.12   $196.10   $196.10  
  Purchase #2 $79.87   13.183%   $90.3993   $90.40   $90.40   $90.40  
  Purchase #3 $155.63   9.634%   $170.6234   $170.62   $170.60   $170.60  
  Purchase #4 $78.33   11.625%   $87.4359   $87.44   $87.45   $87.40  
  Purchase #5 $48.91   8.194%   $52.9177   $52.92   $52.90   $52.90  
  Purchase #6 $213.48   11.192%   $237.3727   $237.37   $237.35   $237.40  
  Purchase #7 $192.48   8.673%   $209.1738   $209.17   $209.15   $209.20  
  7 purchase totals = $944.08       $1,044.0380   $1,044.04   $1,043.95   $1,044.00