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 $186.93   11.371%   $208.1858   $208.19   $208.20   $208.20  
  Purchase #2 $174.50   9.622%   $191.2904   $191.29   $191.30   $191.30  
  Purchase #3 $13.52   8.846%   $14.716   $14.72   $14.70   $14.70  
  Purchase #4 $198.68   6.516%   $211.626   $211.63   $211.65   $211.60  
  Purchase #5 $22.42   11.157%   $24.9214   $24.92   $24.90   $24.90  
  Purchase #6 $109.51   7.529%   $117.755   $117.76   $117.75   $117.80  
  Purchase #7 $239.62   13.802%   $272.6924   $272.69   $272.70   $272.70  
  7 purchase totals = $945.18       $1,041.1870   $1,041.20   $1,041.20   $1,041.20