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 $67.57   10.169%   $74.4412   $74.44   $74.45   $74.40  
  Purchase #2 $181.96   6.752%   $194.2459   $194.25   $194.25   $194.20  
  Purchase #3 $65.35   8.178%   $70.6943   $70.69   $70.70   $70.70  
  Purchase #4 $185.30   6.733%   $197.7762   $197.78   $197.80   $197.80  
  Purchase #5 $43.74   5.246%   $46.0346   $46.03   $46.05   $46.00  
  Purchase #6 $182.30   13.571%   $207.0399   $207.04   $207.05   $207.00  
  Purchase #7 $225.34   5.595%   $237.9478   $237.95   $237.95   $237.90  
  7 purchase totals = $951.56       $1,028.1799   $1,028.18   $1,028.25   $1,028.00