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 $215.92   11.755%   $241.3014   $241.30   $241.30   $241.30  
  Purchase #2 $75.53   12.524%   $84.9894   $84.99   $85.00   $85.00  
  Purchase #3 $162.69   6.133%   $172.6678   $172.67   $172.65   $172.70  
  Purchase #4 $239.51   4.239%   $249.6628   $249.66   $249.65   $249.70  
  Purchase #5 $151.63   6.141%   $160.9416   $160.94   $160.95   $160.90  
  Purchase #6 $36.71   11.233%   $40.8336   $40.83   $40.85   $40.80  
  Purchase #7 $168.41   13.666%   $191.4249   $191.42   $191.40   $191.40  
  7 purchase totals = $1,050.40       $1,141.8215   $1,141.81   $1,141.80   $1,141.80