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 $213.79   10.383%   $235.9878   $235.99   $236.00   $236.00  
  Purchase #2 $169.71   9.273%   $185.4472   $185.45   $185.45   $185.40  
  Purchase #3 $100.51   3.726%   $104.255   $104.26   $104.25   $104.30  
  Purchase #4 $96.74   11.117%   $107.4946   $107.49   $107.50   $107.50  
  Purchase #5 $216.26   5.186%   $227.4752   $227.48   $227.50   $227.50  
  Purchase #6 $172.84   12.270%   $194.0475   $194.05   $194.05   $194.00  
  Purchase #7 $59.74   8.652%   $64.9087   $64.91   $64.90   $64.90  
  7 purchase totals = $1,029.59       $1,119.6160   $1,119.63   $1,119.65   $1,119.60