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 $200.63   13.615%   $227.9458   $227.95   $227.95   $227.90  
  Purchase #2 $71.75   8.305%   $77.7088   $77.71   $77.70   $77.70  
  Purchase #3 $94.76   11.106%   $105.284   $105.28   $105.30   $105.30  
  Purchase #4 $199.95   5.823%   $211.5931   $211.59   $211.60   $211.60  
  Purchase #5 $153.39   3.336%   $158.5071   $158.51   $158.50   $158.50  
  Purchase #6 $69.60   3.693%   $72.1703   $72.17   $72.15   $72.20  
  Purchase #7 $227.33   12.166%   $254.987   $254.99   $255.00   $255.00  
  7 purchase totals = $1,017.41       $1,108.1961   $1,108.20   $1,108.20   $1,108.20