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 $102.59   13.229%   $116.1616   $116.16   $116.15   $116.20  
  Purchase #2 $169.31   6.557%   $180.4117   $180.41   $180.40   $180.40  
  Purchase #3 $96.95   12.229%   $108.806   $108.81   $108.80   $108.80  
  Purchase #4 $249.25   9.338%   $272.525   $272.53   $272.55   $272.50  
  Purchase #5 $241.63   4.579%   $252.6942   $252.69   $252.70   $252.70  
  Purchase #6 $214.64   12.306%   $241.0536   $241.05   $241.05   $241.10  
  Purchase #7 $199.32   6.804%   $212.8817   $212.88   $212.90   $212.90  
  7 purchase totals = $1,273.69       $1,384.5338   $1,384.53   $1,384.55   $1,384.60