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 $67.74   12.556%   $76.2454   $76.25   $76.25   $76.20  
  Purchase #2 $22.62   9.693%   $24.8126   $24.81   $24.80   $24.80  
  Purchase #3 $61.85   5.292%   $65.1231   $65.12   $65.10   $65.10  
  Purchase #4 $73.95   4.669%   $77.4027   $77.40   $77.40   $77.40  
  Purchase #5 $54.72   4.652%   $57.2656   $57.27   $57.25   $57.30  
  Purchase #6 $141.47   9.564%   $155.0002   $155.00   $155.00   $155.00  
  Purchase #7 $153.86   3.218%   $158.8112   $158.81   $158.80   $158.80  
  7 purchase totals = $576.21       $614.6608   $614.66   $614.60   $614.60