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 $217.86   13.491%   $247.2515   $247.25   $247.25   $247.30  
  Purchase #2 $197.70   3.613%   $204.8429   $204.84   $204.85   $204.80  
  Purchase #3 $117.50   3.852%   $122.0261   $122.03   $122.05   $122.00  
  Purchase #4 $92.40   3.144%   $95.3051   $95.31   $95.30   $95.30  
  Purchase #5 $130.77   13.552%   $148.492   $148.49   $148.50   $148.50  
  Purchase #6 $11.98   6.102%   $12.711   $12.71   $12.70   $12.70  
  Purchase #7 $62.38   12.503%   $70.1794   $70.18   $70.20   $70.20  
  7 purchase totals = $830.59       $900.8080   $900.81   $900.85   $900.80