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 $60.52   10.186%   $66.6846   $66.68   $66.70   $66.70  
  Purchase #2 $154.94   8.650%   $168.3423   $168.34   $168.35   $168.30  
  Purchase #3 $108.28   13.131%   $122.4982   $122.50   $122.50   $122.50  
  Purchase #4 $66.52   3.745%   $69.0112   $69.01   $69.00   $69.00  
  Purchase #5 $179.46   11.137%   $199.4465   $199.45   $199.45   $199.40  
  Purchase #6 $235.33   5.193%   $247.5507   $247.55   $247.55   $247.60  
  Purchase #7 $134.27   11.348%   $149.507   $149.51   $149.50   $149.50  
  7 purchase totals = $939.32       $1,023.0405   $1,023.04   $1,023.05   $1,023.00