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 $189.94   12.832%   $214.3131   $214.31   $214.30   $214.30  
  Purchase #2 $58.26   11.574%   $65.003   $65.00   $65.00   $65.00  
  Purchase #3 $134.77   3.803%   $139.8953   $139.90   $139.90   $139.90  
  Purchase #4 $46.25   10.374%   $51.048   $51.05   $51.05   $51.00  
  Purchase #5 $214.94   5.441%   $226.6349   $226.63   $226.65   $226.60  
  Purchase #6 $29.91   12.613%   $33.6825   $33.68   $33.70   $33.70  
  Purchase #7 $130.56   4.387%   $136.2877   $136.29   $136.30   $136.30  
  7 purchase totals = $804.63       $866.8645   $866.86   $866.90   $866.80