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 $134.38   6.565%   $143.202   $143.20   $143.20   $143.20  
  Purchase #2 $27.42   9.465%   $30.0153   $30.02   $30.00   $30.00  
  Purchase #3 $21.59   11.535%   $24.0804   $24.08   $24.10   $24.10  
  Purchase #4 $115.89   4.130%   $120.6763   $120.68   $120.70   $120.70  
  Purchase #5 $60.65   12.832%   $68.4326   $68.43   $68.45   $68.40  
  Purchase #6 $217.59   6.809%   $232.4057   $232.41   $232.40   $232.40  
  Purchase #7 $12.47   9.763%   $13.6874   $13.69   $13.70   $13.70  
  7 purchase totals = $589.99       $632.4997   $632.51   $632.55   $632.50