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 $239.42   7.809%   $258.1163   $258.12   $258.10   $258.10  
  Purchase #2 $67.43   10.254%   $74.3443   $74.34   $74.35   $74.30  
  Purchase #3 $245.76   5.261%   $258.6894   $258.69   $258.70   $258.70  
  Purchase #4 $199.76   8.343%   $216.426   $216.43   $216.45   $216.40  
  Purchase #5 $170.75   13.383%   $193.6015   $193.60   $193.60   $193.60  
  Purchase #6 $217.61   12.850%   $245.5729   $245.57   $245.55   $245.60  
  Purchase #7 $208.95   4.135%   $217.5901   $217.59   $217.60   $217.60  
  7 purchase totals = $1,349.68       $1,464.3405   $1,464.34   $1,464.35   $1,464.30