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 $219.83   10.368%   $242.622   $242.62   $242.60   $242.60  
  Purchase #2 $210.65   12.692%   $237.3857   $237.39   $237.40   $237.40  
  Purchase #3 $191.93   12.482%   $215.8867   $215.89   $215.90   $215.90  
  Purchase #4 $67.90   9.373%   $74.2643   $74.26   $74.25   $74.30  
  Purchase #5 $118.93   12.760%   $134.1055   $134.11   $134.10   $134.10  
  Purchase #6 $186.74   12.418%   $209.9294   $209.93   $209.95   $209.90  
  Purchase #7 $113.55   4.520%   $118.6825   $118.68   $118.70   $118.70  
  7 purchase totals = $1,109.53       $1,232.8761   $1,232.88   $1,232.90   $1,232.90