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 $65.79   8.243%   $71.2131   $71.21   $71.20   $71.20  
  Purchase #2 $222.82   7.513%   $239.5605   $239.56   $239.55   $239.60  
  Purchase #3 $29.94   9.348%   $32.7388   $32.74   $32.75   $32.70  
  Purchase #4 $23.87   4.613%   $24.9711   $24.97   $24.95   $25.00  
  Purchase #5 $245.96   6.399%   $261.699   $261.70   $261.70   $261.70  
  Purchase #6 $168.74   9.202%   $184.2675   $184.27   $184.25   $184.30  
  Purchase #7 $13.92   10.534%   $15.3863   $15.39   $15.40   $15.40  
  7 purchase totals = $771.04       $829.8363   $829.84   $829.80   $829.90