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 $135.99   3.411%   $140.6286   $140.63   $140.65   $140.60  
  Purchase #2 $84.76   13.117%   $95.878   $95.88   $95.90   $95.90  
  Purchase #3 $52.47   13.574%   $59.5923   $59.59   $59.60   $59.60  
  Purchase #4 $140.78   6.112%   $149.3845   $149.38   $149.40   $149.40  
  Purchase #5 $242.50   11.230%   $269.7328   $269.73   $269.75   $269.70  
  Purchase #6 $243.62   6.300%   $258.9681   $258.97   $258.95   $259.00  
  Purchase #7 $30.55   5.719%   $32.2972   $32.30   $32.30   $32.30  
  7 purchase totals = $930.67       $1,006.4815   $1,006.48   $1,006.55   $1,006.50