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 $188.70   9.709%   $207.0209   $207.02   $207.00   $207.00  
  Purchase #2 $8.96   4.413%   $9.3554   $9.36   $9.35   $9.40  
  Purchase #3 $40.63   3.715%   $42.1394   $42.14   $42.15   $42.10  
  Purchase #4 $141.68   9.851%   $155.6369   $155.64   $155.65   $155.60  
  Purchase #5 $234.63   13.190%   $265.5777   $265.58   $265.60   $265.60  
  Purchase #6 $173.76   9.564%   $190.3784   $190.38   $190.40   $190.40  
  Purchase #7 $190.32   8.283%   $206.0842   $206.08   $206.10   $206.10  
  7 purchase totals = $978.68       $1,076.1929   $1,076.20   $1,076.25   $1,076.20