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 $234.92   11.399%   $261.6985   $261.70   $261.70   $261.70  
  Purchase #2 $226.67   3.219%   $233.9665   $233.97   $233.95   $234.00  
  Purchase #3 $22.54   6.348%   $23.9708   $23.97   $23.95   $24.00  
  Purchase #4 $77.91   5.559%   $82.241   $82.24   $82.25   $82.20  
  Purchase #5 $25.71   6.753%   $27.4462   $27.45   $27.45   $27.40  
  Purchase #6 $73.85   10.732%   $81.7756   $81.78   $81.80   $81.80  
  Purchase #7 $233.49   8.103%   $252.4097   $252.41   $252.40   $252.40  
  7 purchase totals = $895.09       $963.5083   $963.52   $963.50   $963.50