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 $52.32   3.293%   $54.0429   $54.04   $54.05   $54.00  
  Purchase #2 $70.63   8.257%   $76.4619   $76.46   $76.45   $76.50  
  Purchase #3 $46.64   4.118%   $48.5606   $48.56   $48.55   $48.60  
  Purchase #4 $133.70   5.646%   $141.2487   $141.25   $141.25   $141.20  
  Purchase #5 $225.39   12.174%   $252.829   $252.83   $252.85   $252.80  
  Purchase #6 $203.77   12.169%   $228.5668   $228.57   $228.55   $228.60  
  Purchase #7 $224.68   5.699%   $237.4845   $237.48   $237.50   $237.50  
  7 purchase totals = $957.13       $1,039.1944   $1,039.19   $1,039.20   $1,039.20