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 $38.82   7.476%   $41.7222   $41.72   $41.70   $41.70  
  Purchase #2 $151.81   7.724%   $163.5358   $163.54   $163.55   $163.50  
  Purchase #3 $82.56   5.627%   $87.2057   $87.21   $87.20   $87.20  
  Purchase #4 $67.97   13.162%   $76.9162   $76.92   $76.90   $76.90  
  Purchase #5 $87.89   7.596%   $94.5661   $94.57   $94.55   $94.60  
  Purchase #6 $213.73   13.471%   $242.5216   $242.52   $242.50   $242.50  
  Purchase #7 $23.25   5.844%   $24.6087   $24.61   $24.60   $24.60  
  7 purchase totals = $666.03       $731.0763   $731.09   $731.00   $731.00