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 $92.60   12.622%   $104.288   $104.29   $104.30   $104.30  
  Purchase #2 $56.93   5.543%   $60.0856   $60.09   $60.10   $60.10  
  Purchase #3 $86.49   11.641%   $96.5583   $96.56   $96.55   $96.60  
  Purchase #4 $249.85   5.235%   $262.9296   $262.93   $262.95   $262.90  
  Purchase #5 $81.87   10.734%   $90.6579   $90.66   $90.65   $90.70  
  Purchase #6 $7.76   4.454%   $8.1056   $8.11   $8.10   $8.10  
  Purchase #7 $88.59   8.350%   $95.9873   $95.99   $96.00   $96.00  
  7 purchase totals = $664.09       $718.6123   $718.63   $718.65   $718.70