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 $243.97   5.654%   $257.7641   $257.76   $257.75   $257.80  
  Purchase #2 $178.51   6.792%   $190.6344   $190.63   $190.65   $190.60  
  Purchase #3 $237.39   3.702%   $246.1782   $246.18   $246.20   $246.20  
  Purchase #4 $68.85   10.821%   $76.3003   $76.30   $76.30   $76.30  
  Purchase #5 $187.81   11.424%   $209.2654   $209.27   $209.25   $209.30  
  Purchase #6 $17.71   6.345%   $18.8337   $18.83   $18.85   $18.80  
  Purchase #7 $44.42   13.457%   $50.3976   $50.40   $50.40   $50.40  
  7 purchase totals = $978.66       $1,049.3737   $1,049.37   $1,049.40   $1,049.40