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 $235.82   11.684%   $263.3732   $263.37   $263.35   $263.40  
  Purchase #2 $237.34   10.166%   $261.468   $261.47   $261.45   $261.50  
  Purchase #3 $214.65   8.748%   $233.4276   $233.43   $233.45   $233.40  
  Purchase #4 $46.57   11.190%   $51.7812   $51.78   $51.80   $51.80  
  Purchase #5 $72.34   13.258%   $81.9308   $81.93   $81.95   $81.90  
  Purchase #6 $43.88   9.336%   $47.9766   $47.98   $48.00   $48.00  
  Purchase #7 $74.34   9.655%   $81.5175   $81.52   $81.50   $81.50  
  7 purchase totals = $924.94       $1,021.4749   $1,021.48   $1,021.50   $1,021.50