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 $66.41   4.282%   $69.2537   $69.25   $69.25   $69.30  
  Purchase #2 $121.83   4.457%   $127.26   $127.26   $127.25   $127.30  
  Purchase #3 $71.75   5.105%   $75.4128   $75.41   $75.40   $75.40  
  Purchase #4 $159.79   7.306%   $171.4643   $171.46   $171.45   $171.50  
  Purchase #5 $207.81   3.223%   $214.5077   $214.51   $214.50   $214.50  
  Purchase #6 $220.35   5.183%   $231.7707   $231.77   $231.75   $231.80  
  Purchase #7 $176.36   8.841%   $191.952   $191.95   $191.95   $192.00  
  7 purchase totals = $1,024.30       $1,081.6212   $1,081.61   $1,081.55   $1,081.80