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 $207.41   9.481%   $227.0745   $227.07   $227.05   $227.10  
  Purchase #2 $96.83   8.330%   $104.8959   $104.90   $104.90   $104.90  
  Purchase #3 $35.59   12.596%   $40.0729   $40.07   $40.05   $40.10  
  Purchase #4 $182.90   5.363%   $192.7089   $192.71   $192.70   $192.70  
  Purchase #5 $12.96   5.409%   $13.661   $13.66   $13.65   $13.70  
  Purchase #6 $206.86   6.603%   $220.519   $220.52   $220.50   $220.50  
  Purchase #7 $168.85   5.502%   $178.1401   $178.14   $178.15   $178.10  
  7 purchase totals = $911.40       $977.0723   $977.07   $977.00   $977.10