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 $209.95   9.581%   $230.0653   $230.07   $230.05   $230.10  
  Purchase #2 $158.92   3.128%   $163.891   $163.89   $163.90   $163.90  
  Purchase #3 $26.37   5.375%   $27.7874   $27.79   $27.80   $27.80  
  Purchase #4 $168.44   5.257%   $177.2949   $177.29   $177.30   $177.30  
  Purchase #5 $110.91   4.320%   $115.7013   $115.70   $115.70   $115.70  
  Purchase #6 $191.41   8.514%   $207.7066   $207.71   $207.70   $207.70  
  Purchase #7 $38.92   11.745%   $43.4912   $43.49   $43.50   $43.50  
  7 purchase totals = $904.92       $965.9377   $965.94   $965.95   $966.00