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 $175.83   13.475%   $199.5231   $199.52   $199.50   $199.50  
  Purchase #2 $54.92   12.131%   $61.5823   $61.58   $61.60   $61.60  
  Purchase #3 $151.49   4.789%   $158.7449   $158.74   $158.75   $158.70  
  Purchase #4 $153.56   5.548%   $162.0795   $162.08   $162.10   $162.10  
  Purchase #5 $15.64   8.219%   $16.9255   $16.93   $16.95   $16.90  
  Purchase #6 $66.39   4.597%   $69.4419   $69.44   $69.45   $69.40  
  Purchase #7 $44.32   11.576%   $49.4505   $49.45   $49.45   $49.50  
  7 purchase totals = $662.15       $717.7477   $717.74   $717.80   $717.70