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 $95.93   11.167%   $106.6425   $106.64   $106.65   $106.60  
  Purchase #2 $59.66   7.389%   $64.0683   $64.07   $64.05   $64.10  
  Purchase #3 $179.49   12.343%   $201.6445   $201.64   $201.65   $201.60  
  Purchase #4 $34.44   6.405%   $36.6459   $36.65   $36.65   $36.60  
  Purchase #5 $62.95   5.609%   $66.4809   $66.48   $66.50   $66.50  
  Purchase #6 $236.51   7.501%   $254.2506   $254.25   $254.25   $254.30  
  Purchase #7 $10.90   3.466%   $11.2778   $11.28   $11.30   $11.30  
  7 purchase totals = $679.88       $741.0105   $741.01   $741.05   $741.00