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 $176.28   9.713%   $193.4021   $193.40   $193.40   $193.40  
  Purchase #2 $231.99   10.153%   $255.5439   $255.54   $255.55   $255.50  
  Purchase #3 $126.71   12.405%   $142.4284   $142.43   $142.45   $142.40  
  Purchase #4 $242.30   9.406%   $265.0907   $265.09   $265.10   $265.10  
  Purchase #5 $58.35   6.115%   $61.9181   $61.92   $61.90   $61.90  
  Purchase #6 $144.50   7.235%   $154.9546   $154.95   $154.95   $155.00  
  Purchase #7 $26.88   5.123%   $28.2571   $28.26   $28.25   $28.30  
  7 purchase totals = $1,007.01       $1,101.5949   $1,101.59   $1,101.60   $1,101.60