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 $212.69   3.726%   $220.6148   $220.61   $220.60   $220.60  
  Purchase #2 $119.70   8.216%   $129.5346   $129.53   $129.55   $129.50  
  Purchase #3 $101.90   5.777%   $107.7868   $107.79   $107.80   $107.80  
  Purchase #4 $71.89   6.584%   $76.6232   $76.62   $76.60   $76.60  
  Purchase #5 $241.65   3.526%   $250.1706   $250.17   $250.15   $250.20  
  Purchase #6 $26.89   13.682%   $30.5691   $30.57   $30.55   $30.60  
  Purchase #7 $189.29   9.171%   $206.6498   $206.65   $206.65   $206.60  
  7 purchase totals = $964.01       $1,021.9489   $1,021.94   $1,021.90   $1,021.90