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 $184.46   6.769%   $196.9461   $196.95   $196.95   $196.90  
  Purchase #2 $222.92   3.468%   $230.6509   $230.65   $230.65   $230.70  
  Purchase #3 $190.55   5.723%   $201.4552   $201.46   $201.45   $201.50  
  Purchase #4 $26.64   12.661%   $30.0129   $30.01   $30.00   $30.00  
  Purchase #5 $235.92   8.215%   $255.3008   $255.30   $255.30   $255.30  
  Purchase #6 $228.65   3.193%   $235.9508   $235.95   $235.95   $236.00  
  Purchase #7 $187.92   13.182%   $212.6916   $212.69   $212.70   $212.70  
  7 purchase totals = $1,277.06       $1,363.0083   $1,363.01   $1,363.00   $1,363.10