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 $186.95   12.551%   $210.4141   $210.41   $210.40   $210.40  
  Purchase #2 $79.71   9.123%   $86.9819   $86.98   $87.00   $87.00  
  Purchase #3 $50.43   11.583%   $56.2713   $56.27   $56.25   $56.30  
  Purchase #4 $151.41   6.757%   $161.6408   $161.64   $161.65   $161.60  
  Purchase #5 $207.25   9.824%   $227.6102   $227.61   $227.60   $227.60  
  Purchase #6 $48.83   6.400%   $51.9551   $51.96   $51.95   $52.00  
  Purchase #7 $125.42   7.481%   $134.8027   $134.80   $134.80   $134.80  
  7 purchase totals = $850.00       $929.6761   $929.67   $929.65   $929.70