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 $245.83   13.759%   $279.6537   $279.65   $279.65   $279.70  
  Purchase #2 $182.53   6.544%   $194.4748   $194.47   $194.45   $194.50  
  Purchase #3 $57.26   5.797%   $60.5794   $60.58   $60.60   $60.60  
  Purchase #4 $109.75   3.867%   $113.994   $113.99   $114.00   $114.00  
  Purchase #5 $183.26   10.865%   $203.1712   $203.17   $203.15   $203.20  
  Purchase #6 $176.39   3.581%   $182.7065   $182.71   $182.70   $182.70  
  Purchase #7 $57.96   5.516%   $61.1571   $61.16   $61.15   $61.20  
  7 purchase totals = $1,012.98       $1,095.7367   $1,095.73   $1,095.70   $1,095.90