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 $116.66   8.371%   $126.4256   $126.43   $126.45   $126.40  
  Purchase #2 $86.57   7.131%   $92.7433   $92.74   $92.75   $92.70  
  Purchase #3 $66.34   10.647%   $73.4032   $73.40   $73.40   $73.40  
  Purchase #4 $212.64   6.371%   $226.1873   $226.19   $226.20   $226.20  
  Purchase #5 $182.54   9.267%   $199.456   $199.46   $199.45   $199.50  
  Purchase #6 $93.54   7.815%   $100.8502   $100.85   $100.85   $100.90  
  Purchase #7 $190.37   7.318%   $204.3013   $204.30   $204.30   $204.30  
  7 purchase totals = $948.66       $1,023.3669   $1,023.37   $1,023.40   $1,023.40