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 $208.36   8.678%   $226.4415   $226.44   $226.45   $226.40  
  Purchase #2 $34.44   10.411%   $38.0255   $38.03   $38.05   $38.00  
  Purchase #3 $122.37   7.564%   $131.6261   $131.63   $131.65   $131.60  
  Purchase #4 $55.75   9.846%   $61.2391   $61.24   $61.25   $61.20  
  Purchase #5 $144.88   7.866%   $156.2763   $156.28   $156.30   $156.30  
  Purchase #6 $104.33   5.440%   $110.0056   $110.01   $110.00   $110.00  
  Purchase #7 $95.76   5.452%   $100.9808   $100.98   $101.00   $101.00  
  7 purchase totals = $765.89       $824.5949   $824.61   $824.70   $824.50