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 $198.71   3.710%   $206.0821   $206.08   $206.10   $206.10  
  Purchase #2 $165.49   8.582%   $179.6924   $179.69   $179.70   $179.70  
  Purchase #3 $88.54   13.441%   $100.4407   $100.44   $100.45   $100.40  
  Purchase #4 $157.89   12.293%   $177.2994   $177.30   $177.30   $177.30  
  Purchase #5 $70.55   9.296%   $77.1083   $77.11   $77.10   $77.10  
  Purchase #6 $163.87   4.179%   $170.7181   $170.72   $170.70   $170.70  
  Purchase #7 $50.96   3.333%   $52.6585   $52.66   $52.65   $52.70  
  7 purchase totals = $896.01       $963.9995   $964.00   $964.00   $964.00