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 $50.99   11.672%   $56.9416   $56.94   $56.95   $56.90  
  Purchase #2 $184.50   13.110%   $208.688   $208.69   $208.70   $208.70  
  Purchase #3 $226.45   13.389%   $256.7694   $256.77   $256.75   $256.80  
  Purchase #4 $182.48   12.668%   $205.5966   $205.60   $205.60   $205.60  
  Purchase #5 $197.99   8.775%   $215.3636   $215.36   $215.35   $215.40  
  Purchase #6 $139.77   5.872%   $147.9773   $147.98   $148.00   $148.00  
  Purchase #7 $163.65   6.497%   $174.2823   $174.28   $174.30   $174.30  
  7 purchase totals = $1,145.83       $1,265.6188   $1,265.62   $1,265.65   $1,265.70