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 $206.96   13.190%   $234.258   $234.26   $234.25   $234.30  
  Purchase #2 $151.34   3.717%   $156.9653   $156.97   $156.95   $157.00  
  Purchase #3 $24.90   4.528%   $26.0275   $26.03   $26.05   $26.00  
  Purchase #4 $76.67   3.856%   $79.6264   $79.63   $79.65   $79.60  
  Purchase #5 $226.84   8.467%   $246.0465   $246.05   $246.05   $246.00  
  Purchase #6 $228.45   12.755%   $257.5888   $257.59   $257.60   $257.60  
  Purchase #7 $6.26   13.597%   $7.1112   $7.11   $7.10   $7.10  
  7 purchase totals = $921.42       $1,007.6237   $1,007.64   $1,007.65   $1,007.60