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 $148.26   5.182%   $155.9428   $155.94   $155.95   $155.90  
  Purchase #2 $98.93   7.841%   $106.6871   $106.69   $106.70   $106.70  
  Purchase #3 $127.61   6.693%   $136.1509   $136.15   $136.15   $136.20  
  Purchase #4 $165.42   5.785%   $174.9895   $174.99   $175.00   $175.00  
  Purchase #5 $49.47   13.374%   $56.0861   $56.09   $56.10   $56.10  
  Purchase #6 $220.73   6.563%   $235.2165   $235.22   $235.20   $235.20  
  Purchase #7 $245.49   13.444%   $278.4937   $278.49   $278.50   $278.50  
  7 purchase totals = $1,055.91       $1,143.5666   $1,143.57   $1,143.60   $1,143.60