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 $138.61   5.602%   $146.3749   $146.37   $146.35   $146.40  
  Purchase #2 $184.67   8.284%   $199.9681   $199.97   $199.95   $200.00  
  Purchase #3 $197.65   3.708%   $204.9789   $204.98   $205.00   $205.00  
  Purchase #4 $235.54   11.358%   $262.2926   $262.29   $262.30   $262.30  
  Purchase #5 $54.89   9.228%   $59.9552   $59.96   $59.95   $60.00  
  Purchase #6 $17.25   10.509%   $19.0628   $19.06   $19.05   $19.10  
  Purchase #7 $131.63   11.457%   $146.7108   $146.71   $146.70   $146.70  
  7 purchase totals = $960.24       $1,039.3433   $1,039.34   $1,039.30   $1,039.50