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 $191.84   6.349%   $204.0199   $204.02   $204.00   $204.00  
  Purchase #2 $61.55   3.154%   $63.4913   $63.49   $63.50   $63.50  
  Purchase #3 $64.76   13.447%   $73.4683   $73.47   $73.45   $73.50  
  Purchase #4 $214.57   10.447%   $236.9861   $236.99   $237.00   $237.00  
  Purchase #5 $134.73   13.159%   $152.4591   $152.46   $152.45   $152.50  
  Purchase #6 $139.67   9.264%   $152.609   $152.61   $152.60   $152.60  
  Purchase #7 $72.83   7.283%   $78.1342   $78.13   $78.15   $78.10  
  7 purchase totals = $879.95       $961.1679   $961.17   $961.15   $961.20