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 $239.87   9.176%   $261.8805   $261.88   $261.90   $261.90  
  Purchase #2 $96.66   11.586%   $107.859   $107.86   $107.85   $107.90  
  Purchase #3 $141.38   11.360%   $157.4408   $157.44   $157.45   $157.40  
  Purchase #4 $182.29   11.118%   $202.557   $202.56   $202.55   $202.60  
  Purchase #5 $196.34   11.680%   $219.2725   $219.27   $219.25   $219.30  
  Purchase #6 $74.86   12.783%   $84.4294   $84.43   $84.45   $84.40  
  Purchase #7 $38.40   8.133%   $41.5231   $41.52   $41.50   $41.50  
  7 purchase totals = $969.80       $1,074.9623   $1,074.96   $1,074.95   $1,075.00