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 $69.61   10.566%   $76.965   $76.97   $76.95   $77.00  
  Purchase #2 $250.64   7.159%   $268.5833   $268.58   $268.60   $268.60  
  Purchase #3 $171.68   6.591%   $182.9954   $183.00   $183.00   $183.00  
  Purchase #4 $87.27   6.509%   $92.9504   $92.95   $92.95   $93.00  
  Purchase #5 $14.93   3.286%   $15.4206   $15.42   $15.40   $15.40  
  Purchase #6 $169.79   12.251%   $190.591   $190.59   $190.60   $190.60  
  Purchase #7 $144.41   11.615%   $161.1832   $161.18   $161.20   $161.20  
  7 purchase totals = $908.33       $988.6889   $988.69   $988.70   $988.80