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 $52.76   8.694%   $57.347   $57.35   $57.35   $57.30  
  Purchase #2 $68.99   11.299%   $76.7852   $76.79   $76.80   $76.80  
  Purchase #3 $242.63   10.748%   $268.7079   $268.71   $268.70   $268.70  
  Purchase #4 $246.79   8.426%   $267.5845   $267.58   $267.60   $267.60  
  Purchase #5 $101.50   13.507%   $115.2096   $115.21   $115.20   $115.20  
  Purchase #6 $133.33   10.742%   $147.6523   $147.65   $147.65   $147.70  
  Purchase #7 $221.54   8.193%   $239.6908   $239.69   $239.70   $239.70  
  7 purchase totals = $1,067.54       $1,172.9773   $1,172.98   $1,173.00   $1,173.00