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 $48.51   6.438%   $51.6331   $51.63   $51.65   $51.60  
  Purchase #2 $215.58   12.580%   $242.7   $242.70   $242.70   $242.70  
  Purchase #3 $217.35   6.280%   $230.9996   $231.00   $231.00   $231.00  
  Purchase #4 $229.99   13.863%   $261.8735   $261.87   $261.85   $261.90  
  Purchase #5 $189.75   3.580%   $196.5431   $196.54   $196.55   $196.50  
  Purchase #6 $242.54   12.238%   $272.222   $272.22   $272.20   $272.20  
  Purchase #7 $161.44   5.721%   $170.676   $170.68   $170.70   $170.70  
  7 purchase totals = $1,305.16       $1,426.6473   $1,426.64   $1,426.65   $1,426.60