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 $143.61   12.458%   $161.5009   $161.50   $161.50   $161.50  
  Purchase #2 $152.58   11.178%   $169.6354   $169.64   $169.65   $169.60  
  Purchase #3 $69.91   9.378%   $76.4662   $76.47   $76.45   $76.50  
  Purchase #4 $163.43   7.634%   $175.9062   $175.91   $175.90   $175.90  
  Purchase #5 $61.62   7.428%   $66.1971   $66.20   $66.20   $66.20  
  Purchase #6 $237.47   5.564%   $250.6828   $250.68   $250.70   $250.70  
  Purchase #7 $147.84   13.158%   $167.2928   $167.29   $167.30   $167.30  
  7 purchase totals = $976.46       $1,067.6814   $1,067.69   $1,067.70   $1,067.70