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 $185.35   11.306%   $206.3057   $206.31   $206.30   $206.30  
  Purchase #2 $171.36   8.284%   $185.5555   $185.56   $185.55   $185.60  
  Purchase #3 $123.50   4.508%   $129.0674   $129.07   $129.05   $129.10  
  Purchase #4 $147.62   10.675%   $163.3784   $163.38   $163.40   $163.40  
  Purchase #5 $68.65   10.763%   $76.0388   $76.04   $76.05   $76.00  
  Purchase #6 $147.94   11.219%   $164.5374   $164.54   $164.55   $164.50  
  Purchase #7 $112.75   9.681%   $123.6653   $123.67   $123.65   $123.70  
  7 purchase totals = $957.17       $1,048.5485   $1,048.57   $1,048.55   $1,048.60