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 $217.88   12.238%   $244.5442   $244.54   $244.55   $244.50  
  Purchase #2 $192.92   13.788%   $219.5198   $219.52   $219.50   $219.50  
  Purchase #3 $125.79   8.438%   $136.4042   $136.40   $136.40   $136.40  
  Purchase #4 $156.25   6.855%   $166.9609   $166.96   $166.95   $167.00  
  Purchase #5 $129.68   3.814%   $134.626   $134.63   $134.65   $134.60  
  Purchase #6 $48.56   13.124%   $54.933   $54.93   $54.95   $54.90  
  Purchase #7 $26.47   5.316%   $27.8771   $27.88   $27.90   $27.90  
  7 purchase totals = $897.55       $984.8652   $984.86   $984.90   $984.80