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 $23.69   6.641%   $25.2633   $25.26   $25.25   $25.30  
  Purchase #2 $180.79   3.580%   $187.2623   $187.26   $187.25   $187.30  
  Purchase #3 $242.52   6.363%   $257.9515   $257.95   $257.95   $258.00  
  Purchase #4 $50.61   5.241%   $53.2625   $53.26   $53.25   $53.30  
  Purchase #5 $158.76   3.478%   $164.2817   $164.28   $164.30   $164.30  
  Purchase #6 $206.93   9.175%   $225.9158   $225.92   $225.90   $225.90  
  Purchase #7 $102.87   4.681%   $107.6853   $107.69   $107.70   $107.70  
  7 purchase totals = $966.17       $1,021.6224   $1,021.62   $1,021.60   $1,021.80