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 $245.63   5.453%   $259.0242   $259.02   $259.00   $259.00  
  Purchase #2 $15.39   4.564%   $16.0924   $16.09   $16.10   $16.10  
  Purchase #3 $239.88   11.413%   $267.2575   $267.26   $267.25   $267.30  
  Purchase #4 $14.92   12.255%   $16.7484   $16.75   $16.75   $16.70  
  Purchase #5 $61.96   6.287%   $65.8554   $65.86   $65.85   $65.90  
  Purchase #6 $245.77   4.398%   $256.579   $256.58   $256.60   $256.60  
  Purchase #7 $87.92   8.466%   $95.3633   $95.36   $95.35   $95.40  
  7 purchase totals = $911.47       $976.9202   $976.92   $976.90   $977.00