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 $195.87   6.811%   $209.2107   $209.21   $209.20   $209.20  
  Purchase #2 $29.83   3.577%   $30.897   $30.90   $30.90   $30.90  
  Purchase #3 $61.83   10.151%   $68.1064   $68.11   $68.10   $68.10  
  Purchase #4 $122.94   4.351%   $128.2891   $128.29   $128.30   $128.30  
  Purchase #5 $211.55   11.827%   $236.57   $236.57   $236.55   $236.60  
  Purchase #6 $54.87   12.385%   $61.6656   $61.67   $61.65   $61.70  
  Purchase #7 $77.28   4.449%   $80.7182   $80.72   $80.70   $80.70  
  7 purchase totals = $754.17       $815.4570   $815.47   $815.40   $815.50