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 $180.86   11.564%   $201.7747   $201.77   $201.75   $201.80  
  Purchase #2 $102.73   8.828%   $111.799   $111.80   $111.80   $111.80  
  Purchase #3 $14.29   8.250%   $15.4689   $15.47   $15.45   $15.50  
  Purchase #4 $151.81   12.742%   $171.1536   $171.15   $171.15   $171.20  
  Purchase #5 $196.70   13.106%   $222.4795   $222.48   $222.50   $222.50  
  Purchase #6 $58.79   3.619%   $60.9176   $60.92   $60.90   $60.90  
  Purchase #7 $226.67   4.833%   $237.625   $237.63   $237.65   $237.60  
  7 purchase totals = $931.85       $1,021.2183   $1,021.22   $1,021.20   $1,021.30