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 $59.88   9.621%   $65.6411   $65.64   $65.65   $65.60  
  Purchase #2 $234.92   6.803%   $250.9016   $250.90   $250.90   $250.90  
  Purchase #3 $74.82   9.723%   $82.0947   $82.09   $82.10   $82.10  
  Purchase #4 $246.61   9.647%   $270.4005   $270.40   $270.40   $270.40  
  Purchase #5 $177.66   12.475%   $199.8231   $199.82   $199.80   $199.80  
  Purchase #6 $108.81   13.430%   $123.4232   $123.42   $123.40   $123.40  
  Purchase #7 $232.26   5.657%   $245.3989   $245.40   $245.40   $245.40  
  7 purchase totals = $1,134.96       $1,237.6831   $1,237.67   $1,237.65   $1,237.60