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 $201.55   10.126%   $221.959   $221.96   $221.95   $222.00  
  Purchase #2 $107.43   4.591%   $112.3621   $112.36   $112.35   $112.40  
  Purchase #3 $70.65   8.850%   $76.9025   $76.90   $76.90   $76.90  
  Purchase #4 $119.81   5.128%   $125.9539   $125.95   $125.95   $126.00  
  Purchase #5 $132.87   9.165%   $145.0475   $145.05   $145.05   $145.00  
  Purchase #6 $79.93   6.265%   $84.9376   $84.94   $84.95   $84.90  
  Purchase #7 $228.62   4.617%   $239.1754   $239.18   $239.20   $239.20  
  7 purchase totals = $940.86       $1,006.3380   $1,006.34   $1,006.35   $1,006.40