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 $148.27   3.856%   $153.9873   $153.99   $154.00   $154.00  
  Purchase #2 $249.77   13.308%   $283.0094   $283.01   $283.00   $283.00  
  Purchase #3 $104.82   13.675%   $119.1541   $119.15   $119.15   $119.20  
  Purchase #4 $168.74   10.242%   $186.0224   $186.02   $186.00   $186.00  
  Purchase #5 $193.38   11.259%   $215.1527   $215.15   $215.15   $215.20  
  Purchase #6 $5.83   12.641%   $6.567   $6.57   $6.55   $6.60  
  Purchase #7 $64.77   3.792%   $67.2261   $67.23   $67.25   $67.20  
  7 purchase totals = $935.58       $1,031.1190   $1,031.12   $1,031.10   $1,031.20