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 $59.29   12.380%   $66.6301   $66.63   $66.65   $66.60  
  Purchase #2 $171.97   13.130%   $194.5497   $194.55   $194.55   $194.50  
  Purchase #3 $230.99   5.339%   $243.3226   $243.32   $243.30   $243.30  
  Purchase #4 $63.62   11.256%   $70.7811   $70.78   $70.80   $70.80  
  Purchase #5 $176.70   10.407%   $195.0892   $195.09   $195.10   $195.10  
  Purchase #6 $170.61   12.565%   $192.0471   $192.05   $192.05   $192.00  
  Purchase #7 $45.41   8.683%   $49.353   $49.35   $49.35   $49.40  
  7 purchase totals = $918.59       $1,011.7728   $1,011.77   $1,011.80   $1,011.70