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 $88.82   4.209%   $92.5584   $92.56   $92.55   $92.60  
  Purchase #2 $136.84   13.433%   $155.2217   $155.22   $155.20   $155.20  
  Purchase #3 $123.73   12.444%   $139.127   $139.13   $139.15   $139.10  
  Purchase #4 $110.51   4.701%   $115.7051   $115.71   $115.70   $115.70  
  Purchase #5 $234.81   7.509%   $252.4419   $252.44   $252.45   $252.40  
  Purchase #6 $196.69   12.703%   $221.6755   $221.68   $221.70   $221.70  
  Purchase #7 $68.58   11.415%   $76.4084   $76.41   $76.40   $76.40  
  7 purchase totals = $959.98       $1,053.1380   $1,053.15   $1,053.15   $1,053.10