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 $236.92   12.540%   $266.6298   $266.63   $266.65   $266.60  
  Purchase #2 $237.89   5.356%   $250.6314   $250.63   $250.65   $250.60  
  Purchase #3 $113.79   11.665%   $127.0636   $127.06   $127.05   $127.10  
  Purchase #4 $88.61   9.777%   $97.2734   $97.27   $97.25   $97.30  
  Purchase #5 $164.64   13.111%   $186.226   $186.23   $186.25   $186.20  
  Purchase #6 $107.47   4.416%   $112.2159   $112.22   $112.20   $112.20  
  Purchase #7 $202.80   12.710%   $228.5759   $228.58   $228.60   $228.60  
  7 purchase totals = $1,152.12       $1,268.6160   $1,268.62   $1,268.65   $1,268.60