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 $19.30   5.823%   $20.4238   $20.42   $20.40   $20.40  
  Purchase #2 $62.92   10.551%   $69.5587   $69.56   $69.55   $69.60  
  Purchase #3 $101.41   8.497%   $110.0268   $110.03   $110.05   $110.00  
  Purchase #4 $153.81   10.828%   $170.4645   $170.46   $170.45   $170.50  
  Purchase #5 $130.93   9.217%   $142.9978   $143.00   $143.00   $143.00  
  Purchase #6 $7.78   13.818%   $8.855   $8.86   $8.85   $8.90  
  Purchase #7 $47.67   13.404%   $54.0597   $54.06   $54.05   $54.10  
  7 purchase totals = $523.82       $576.3863   $576.39   $576.35   $576.50