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 $191.99   8.773%   $208.8333   $208.83   $208.85   $208.80  
  Purchase #2 $36.59   12.536%   $41.1769   $41.18   $41.20   $41.20  
  Purchase #3 $71.41   4.383%   $74.5399   $74.54   $74.55   $74.50  
  Purchase #4 $230.29   9.781%   $252.8147   $252.81   $252.80   $252.80  
  Purchase #5 $175.96   5.611%   $185.8331   $185.83   $185.85   $185.80  
  Purchase #6 $121.80   8.133%   $131.706   $131.71   $131.70   $131.70  
  Purchase #7 $112.48   6.315%   $119.5831   $119.58   $119.60   $119.60  
  7 purchase totals = $940.52       $1,014.4870   $1,014.48   $1,014.55   $1,014.40