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 $247.35   7.724%   $266.4553   $266.46   $266.45   $266.50  
  Purchase #2 $186.62   3.593%   $193.3253   $193.33   $193.35   $193.30  
  Purchase #3 $18.37   5.572%   $19.3936   $19.39   $19.40   $19.40  
  Purchase #4 $124.38   9.158%   $135.7707   $135.77   $135.75   $135.80  
  Purchase #5 $62.68   13.170%   $70.935   $70.94   $70.95   $70.90  
  Purchase #6 $217.51   7.422%   $233.6536   $233.65   $233.65   $233.70  
  Purchase #7 $166.94   6.254%   $177.3804   $177.38   $177.40   $177.40  
  7 purchase totals = $1,023.85       $1,096.9139   $1,096.92   $1,096.95   $1,097.00