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 $51.32   4.202%   $53.4765   $53.48   $53.50   $53.50  
  Purchase #2 $196.35   6.144%   $208.4137   $208.41   $208.40   $208.40  
  Purchase #3 $51.56   13.460%   $58.5   $58.50   $58.50   $58.50  
  Purchase #4 $203.83   11.548%   $227.3683   $227.37   $227.35   $227.40  
  Purchase #5 $36.95   4.739%   $38.7011   $38.70   $38.70   $38.70  
  Purchase #6 $212.33   12.299%   $238.4445   $238.44   $238.45   $238.40  
  Purchase #7 $241.62   5.120%   $253.9909   $253.99   $254.00   $254.00  
  7 purchase totals = $993.96       $1,078.8950   $1,078.89   $1,078.90   $1,078.90