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 $54.90   13.564%   $62.3466   $62.35   $62.35   $62.30  
  Purchase #2 $119.96   10.478%   $132.5294   $132.53   $132.55   $132.50  
  Purchase #3 $141.60   8.606%   $153.7861   $153.79   $153.80   $153.80  
  Purchase #4 $45.78   11.587%   $51.0845   $51.08   $51.10   $51.10  
  Purchase #5 $140.98   8.403%   $152.8265   $152.83   $152.85   $152.80  
  Purchase #6 $213.49   10.326%   $235.535   $235.54   $235.55   $235.50  
  Purchase #7 $72.46   7.313%   $77.759   $77.76   $77.75   $77.80  
  7 purchase totals = $789.17       $865.8671   $865.88   $865.95   $865.80