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 $211.37   11.699%   $236.0982   $236.10   $236.10   $236.10  
  Purchase #2 $102.95   13.281%   $116.6228   $116.62   $116.60   $116.60  
  Purchase #3 $50.81   6.771%   $54.2503   $54.25   $54.25   $54.30  
  Purchase #4 $85.94   3.339%   $88.8095   $88.81   $88.80   $88.80  
  Purchase #5 $177.85   11.771%   $198.7847   $198.78   $198.80   $198.80  
  Purchase #6 $40.70   5.268%   $42.8441   $42.84   $42.85   $42.80  
  Purchase #7 $226.89   3.224%   $234.2049   $234.20   $234.20   $234.20  
  7 purchase totals = $896.51       $971.6145   $971.60   $971.60   $971.60