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 $39.27   13.865%   $44.7148   $44.71   $44.70   $44.70  
  Purchase #2 $200.75   3.138%   $207.0495   $207.05   $207.05   $207.00  
  Purchase #3 $218.59   13.229%   $247.5073   $247.51   $247.50   $247.50  
  Purchase #4 $11.64   8.626%   $12.6441   $12.64   $12.65   $12.60  
  Purchase #5 $188.55   11.486%   $210.2069   $210.21   $210.20   $210.20  
  Purchase #6 $101.39   9.177%   $110.6946   $110.69   $110.70   $110.70  
  Purchase #7 $179.86   3.195%   $185.6065   $185.61   $185.60   $185.60  
  7 purchase totals = $940.05       $1,018.4237   $1,018.42   $1,018.40   $1,018.30