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 $104.95   7.256%   $112.5652   $112.57   $112.55   $112.60  
  Purchase #2 $163.31   10.642%   $180.6895   $180.69   $180.70   $180.70  
  Purchase #3 $141.40   8.852%   $153.9167   $153.92   $153.90   $153.90  
  Purchase #4 $33.55   10.463%   $37.0603   $37.06   $37.05   $37.10  
  Purchase #5 $23.63   11.124%   $26.2586   $26.26   $26.25   $26.30  
  Purchase #6 $110.45   11.703%   $123.376   $123.38   $123.40   $123.40  
  Purchase #7 $200.48   7.245%   $215.0048   $215.00   $215.00   $215.00  
  7 purchase totals = $777.77       $848.8711   $848.88   $848.85   $849.00