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 $60.61   12.546%   $68.2141   $68.21   $68.20   $68.20  
  Purchase #2 $73.54   3.247%   $75.9278   $75.93   $75.95   $75.90  
  Purchase #3 $58.96   4.550%   $61.6427   $61.64   $61.65   $61.60  
  Purchase #4 $139.43   12.282%   $156.5548   $156.55   $156.55   $156.60  
  Purchase #5 $91.27   10.589%   $100.9346   $100.93   $100.95   $100.90  
  Purchase #6 $248.70   12.772%   $280.464   $280.46   $280.45   $280.50  
  Purchase #7 $192.35   10.738%   $213.0045   $213.00   $213.00   $213.00  
  7 purchase totals = $864.86       $956.7425   $956.72   $956.75   $956.70