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 $200.87   5.184%   $211.2831   $211.28   $211.30   $211.30  
  Purchase #2 $210.79   11.629%   $235.3028   $235.30   $235.30   $235.30  
  Purchase #3 $65.63   11.366%   $73.0895   $73.09   $73.10   $73.10  
  Purchase #4 $26.90   12.314%   $30.2125   $30.21   $30.20   $30.20  
  Purchase #5 $59.45   11.360%   $66.2035   $66.20   $66.20   $66.20  
  Purchase #6 $63.36   5.617%   $66.9189   $66.92   $66.90   $66.90  
  Purchase #7 $116.51   6.252%   $123.7942   $123.79   $123.80   $123.80  
  7 purchase totals = $743.51       $806.8045   $806.79   $806.80   $806.80