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 $246.92   8.790%   $268.6243   $268.62   $268.60   $268.60  
  Purchase #2 $82.42   13.657%   $93.6761   $93.68   $93.70   $93.70  
  Purchase #3 $245.80   5.767%   $259.9753   $259.98   $260.00   $260.00  
  Purchase #4 $208.93   12.223%   $234.4675   $234.47   $234.45   $234.50  
  Purchase #5 $43.64   6.198%   $46.3448   $46.34   $46.35   $46.30  
  Purchase #6 $121.46   12.818%   $137.0287   $137.03   $137.05   $137.00  
  Purchase #7 $120.78   5.872%   $127.8722   $127.87   $127.85   $127.90  
  7 purchase totals = $1,069.95       $1,167.9889   $1,167.99   $1,168.00   $1,168.00