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 $52.65   6.746%   $56.2018   $56.20   $56.20   $56.20  
  Purchase #2 $204.86   12.268%   $229.9922   $229.99   $230.00   $230.00  
  Purchase #3 $238.57   9.616%   $261.5109   $261.51   $261.50   $261.50  
  Purchase #4 $150.86   6.870%   $161.2241   $161.22   $161.20   $161.20  
  Purchase #5 $24.49   4.570%   $25.6092   $25.61   $25.60   $25.60  
  Purchase #6 $113.31   12.262%   $127.2041   $127.20   $127.20   $127.20  
  Purchase #7 $138.99   13.699%   $158.0302   $158.03   $158.05   $158.00  
  7 purchase totals = $923.73       $1,019.7725   $1,019.76   $1,019.75   $1,019.70