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   11.116%   $262.0338   $262.03   $262.05   $262.00  
  Purchase #2 $172.28   10.461%   $190.3022   $190.30   $190.30   $190.30  
  Purchase #3 $46.81   11.251%   $52.0766   $52.08   $52.10   $52.10  
  Purchase #4 $106.33   8.564%   $115.4361   $115.44   $115.45   $115.40  
  Purchase #5 $134.64   6.859%   $143.875   $143.88   $143.90   $143.90  
  Purchase #6 $92.81   5.519%   $97.9322   $97.93   $97.95   $97.90  
  Purchase #7 $95.92   9.398%   $104.9346   $104.93   $104.95   $104.90  
  7 purchase totals = $884.61       $966.5905   $966.59   $966.70   $966.50