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 $51.94   7.822%   $56.0027   $56.00   $56.00   $56.00  
  Purchase #2 $37.75   10.748%   $41.8074   $41.81   $41.80   $41.80  
  Purchase #3 $104.67   13.349%   $118.6424   $118.64   $118.65   $118.60  
  Purchase #4 $203.90   9.760%   $223.8006   $223.80   $223.80   $223.80  
  Purchase #5 $242.83   7.566%   $261.2025   $261.20   $261.20   $261.20  
  Purchase #6 $136.67   12.772%   $154.1255   $154.13   $154.15   $154.10  
  Purchase #7 $35.47   11.382%   $39.5072   $39.51   $39.50   $39.50  
  7 purchase totals = $813.23       $895.0883   $895.09   $895.10   $895.00