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 $247.90   5.596%   $261.7725   $261.77   $261.75   $261.80  
  Purchase #2 $228.28   3.353%   $235.9342   $235.93   $235.95   $235.90  
  Purchase #3 $245.54   13.335%   $278.2828   $278.28   $278.30   $278.30  
  Purchase #4 $48.91   13.216%   $55.3739   $55.37   $55.35   $55.40  
  Purchase #5 $182.54   3.106%   $188.2097   $188.21   $188.20   $188.20  
  Purchase #6 $94.69   12.282%   $106.3198   $106.32   $106.30   $106.30  
  Purchase #7 $172.40   7.543%   $185.4041   $185.40   $185.40   $185.40  
  7 purchase totals = $1,220.26       $1,311.2970   $1,311.28   $1,311.25   $1,311.30