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 $62.79   9.275%   $68.6138   $68.61   $68.60   $68.60  
  Purchase #2 $164.93   11.689%   $184.2087   $184.21   $184.20   $184.20  
  Purchase #3 $116.65   6.849%   $124.6394   $124.64   $124.65   $124.60  
  Purchase #4 $73.60   5.672%   $77.7746   $77.77   $77.75   $77.80  
  Purchase #5 $224.44   6.509%   $239.0488   $239.05   $239.05   $239.00  
  Purchase #6 $225.32   13.589%   $255.9387   $255.94   $255.95   $255.90  
  Purchase #7 $75.59   5.219%   $79.535   $79.54   $79.55   $79.50  
  7 purchase totals = $943.32       $1,029.7590   $1,029.76   $1,029.75   $1,029.60