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 $136.69   3.844%   $141.9444   $141.94   $141.95   $141.90  
  Purchase #2 $187.42   4.631%   $196.0994   $196.10   $196.10   $196.10  
  Purchase #3 $22.68   8.371%   $24.5785   $24.58   $24.60   $24.60  
  Purchase #4 $205.74   11.771%   $229.9577   $229.96   $229.95   $230.00  
  Purchase #5 $23.63   3.133%   $24.3703   $24.37   $24.35   $24.40  
  Purchase #6 $222.41   6.134%   $236.0526   $236.05   $236.05   $236.10  
  Purchase #7 $22.70   11.152%   $25.2315   $25.23   $25.25   $25.20  
  7 purchase totals = $821.27       $878.2344   $878.23   $878.25   $878.30