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 $249.98   4.787%   $261.9465   $261.95   $261.95   $261.90  
  Purchase #2 $75.78   10.564%   $83.7854   $83.79   $83.80   $83.80  
  Purchase #3 $175.98   9.379%   $192.4852   $192.49   $192.50   $192.50  
  Purchase #4 $96.98   6.564%   $103.3458   $103.35   $103.35   $103.30  
  Purchase #5 $189.67   3.855%   $196.9818   $196.98   $197.00   $197.00  
  Purchase #6 $199.98   10.725%   $221.4279   $221.43   $221.45   $221.40  
  Purchase #7 $139.32   5.170%   $146.5228   $146.52   $146.50   $146.50  
  7 purchase totals = $1,127.69       $1,206.4954   $1,206.51   $1,206.55   $1,206.40