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 $247.83   5.717%   $261.9984   $262.00   $262.00   $262.00  
  Purchase #2 $70.38   6.217%   $74.7555   $74.76   $74.75   $74.80  
  Purchase #3 $203.40   9.227%   $222.1677   $222.17   $222.15   $222.20  
  Purchase #4 $162.76   13.585%   $184.8709   $184.87   $184.85   $184.90  
  Purchase #5 $208.80   8.404%   $226.3476   $226.35   $226.35   $226.30  
  Purchase #6 $17.80   8.373%   $19.2904   $19.29   $19.30   $19.30  
  Purchase #7 $74.35   13.111%   $84.098   $84.10   $84.10   $84.10  
  7 purchase totals = $985.32       $1,073.5285   $1,073.54   $1,073.50   $1,073.60