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 $191.66   11.646%   $213.9807   $213.98   $214.00   $214.00  
  Purchase #2 $242.55   8.787%   $263.8629   $263.86   $263.85   $263.90  
  Purchase #3 $240.59   3.197%   $248.2817   $248.28   $248.30   $248.30  
  Purchase #4 $196.51   3.611%   $203.606   $203.61   $203.60   $203.60  
  Purchase #5 $69.36   5.225%   $72.9841   $72.98   $73.00   $73.00  
  Purchase #6 $131.79   7.655%   $141.8785   $141.88   $141.90   $141.90  
  Purchase #7 $115.90   6.497%   $123.43   $123.43   $123.45   $123.40  
  7 purchase totals = $1,188.36       $1,268.0239   $1,268.02   $1,268.10   $1,268.10