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 $16.85   13.752%   $19.1672   $19.17   $19.15   $19.20  
  Purchase #2 $182.30   6.288%   $193.763   $193.76   $193.75   $193.80  
  Purchase #3 $88.79   3.747%   $92.117   $92.12   $92.10   $92.10  
  Purchase #4 $115.69   12.446%   $130.0888   $130.09   $130.10   $130.10  
  Purchase #5 $103.85   11.496%   $115.7886   $115.79   $115.80   $115.80  
  Purchase #6 $165.37   13.716%   $188.0521   $188.05   $188.05   $188.10  
  Purchase #7 $248.25   13.225%   $281.0811   $281.08   $281.10   $281.10  
  7 purchase totals = $921.10       $1,020.0578   $1,020.06   $1,020.05   $1,020.20