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 $55.40   11.159%   $61.5821   $61.58   $61.60   $61.60  
  Purchase #2 $116.39   7.290%   $124.8748   $124.87   $124.85   $124.90  
  Purchase #3 $12.49   4.721%   $13.0797   $13.08   $13.10   $13.10  
  Purchase #4 $86.66   7.354%   $93.033   $93.03   $93.05   $93.00  
  Purchase #5 $227.55   13.249%   $257.6981   $257.70   $257.70   $257.70  
  Purchase #6 $60.26   8.648%   $65.4713   $65.47   $65.45   $65.50  
  Purchase #7 $55.93   11.800%   $62.5297   $62.53   $62.55   $62.50  
  7 purchase totals = $614.68       $678.2687   $678.26   $678.30   $678.30