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 $242.81   12.621%   $273.4551   $273.46   $273.45   $273.50  
  Purchase #2 $138.64   4.343%   $144.6611   $144.66   $144.65   $144.70  
  Purchase #3 $55.40   4.609%   $57.9534   $57.95   $57.95   $58.00  
  Purchase #4 $70.29   12.730%   $79.2379   $79.24   $79.25   $79.20  
  Purchase #5 $171.72   6.735%   $183.2853   $183.29   $183.30   $183.30  
  Purchase #6 $236.71   5.149%   $248.8982   $248.90   $248.90   $248.90  
  Purchase #7 $58.26   3.515%   $60.3078   $60.31   $60.30   $60.30  
  7 purchase totals = $973.83       $1,047.7988   $1,047.81   $1,047.80   $1,047.90