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 $39.63   4.850%   $41.5521   $41.55   $41.55   $41.60  
  Purchase #2 $177.68   10.149%   $195.7127   $195.71   $195.70   $195.70  
  Purchase #3 $151.34   4.683%   $158.4273   $158.43   $158.45   $158.40  
  Purchase #4 $101.52   3.163%   $104.7311   $104.73   $104.75   $104.70  
  Purchase #5 $158.55   13.274%   $179.5959   $179.60   $179.60   $179.60  
  Purchase #6 $94.31   7.245%   $101.1428   $101.14   $101.15   $101.10  
  Purchase #7 $206.93   13.238%   $234.3234   $234.32   $234.30   $234.30  
  7 purchase totals = $929.96       $1,015.4853   $1,015.48   $1,015.50   $1,015.40