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 $56.65   5.337%   $59.6734   $59.67   $59.65   $59.70  
  Purchase #2 $224.89   6.688%   $239.9306   $239.93   $239.95   $239.90  
  Purchase #3 $146.31   12.553%   $164.6763   $164.68   $164.70   $164.70  
  Purchase #4 $62.95   6.452%   $67.0115   $67.01   $67.00   $67.00  
  Purchase #5 $233.86   10.142%   $257.5781   $257.58   $257.60   $257.60  
  Purchase #6 $65.73   3.473%   $68.0128   $68.01   $68.00   $68.00  
  Purchase #7 $149.50   9.497%   $163.698   $163.70   $163.70   $163.70  
  7 purchase totals = $939.89       $1,020.5807   $1,020.58   $1,020.60   $1,020.60