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 $208.83   13.382%   $236.7756   $236.78   $236.80   $236.80  
  Purchase #2 $187.81   4.180%   $195.6605   $195.66   $195.65   $195.70  
  Purchase #3 $49.87   11.387%   $55.5487   $55.55   $55.55   $55.50  
  Purchase #4 $133.51   10.786%   $147.9104   $147.91   $147.90   $147.90  
  Purchase #5 $188.84   4.710%   $197.7344   $197.73   $197.75   $197.70  
  Purchase #6 $204.99   7.829%   $221.0387   $221.04   $221.05   $221.00  
  Purchase #7 $70.99   12.546%   $79.8964   $79.90   $79.90   $79.90  
  7 purchase totals = $1,044.84       $1,134.5647   $1,134.57   $1,134.60   $1,134.50