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 $57.92   8.824%   $63.0309   $63.03   $63.05   $63.00  
  Purchase #2 $142.29   6.235%   $151.1618   $151.16   $151.15   $151.20  
  Purchase #3 $249.74   9.212%   $272.746   $272.75   $272.75   $272.70  
  Purchase #4 $67.66   4.723%   $70.8556   $70.86   $70.85   $70.90  
  Purchase #5 $114.95   6.231%   $122.1125   $122.11   $122.10   $122.10  
  Purchase #6 $231.85   13.837%   $263.9311   $263.93   $263.95   $263.90  
  Purchase #7 $104.70   8.446%   $113.543   $113.54   $113.55   $113.50  
  7 purchase totals = $969.11       $1,057.3809   $1,057.38   $1,057.40   $1,057.30